Summary at a glance
Goal: Expand efficiently without triggering catastrophic coalition wars.
Do this first:
- Monitor AE regularly (check at 30-40 AE, not 50+)
- Use Reconquest CB whenever possible (-50% AE)
- Improve relations with high-AE nations
Pitfall to avoid: Expanding too fast early game leads to late-game coalition disasters. Slow and steady wins.
Aggressive Expansion (AE) is the primary constraint on expansion speed in EU5. Understanding how to manage AE prevents catastrophic coalition wars that can destroy your empire.
What is Aggressive Expansion?
Aggressive Expansion represents international outrage at your conquests. High AE causes nations to form coalitions against you.
How AE Works
When You Gain AE:
- Conquering provinces in wars
- Forcing vassalization
- Breaking treaties or truces
- Demanding excessive peace terms
- Taking land from allies/subjects
AE Magnitude Factors:
- Base AE: Each province generates 5-15 AE
- Development: Higher development = more AE (cities generate 2-3x more than rural)
- Distance: Nearby nations get more AE than distant ones
- Religion/Culture: Same religion/culture = 50% more AE
- HRE Membership: Taking HRE land generates massive AE in all HRE members
- Co-belligerents: Nations you drag into wars get less AE
AE Decay
Decay Rate: -2 to -4 AE per year (base)
Modified By:
- Diplomatic reputation: +0.5 to +1 decay per year
- Prestige: +0.2 to +0.5 decay per year
- Improving relations: +1 AE decay per year (with that nation only)
- Time: AE naturally decays over 10-20 years
Coalition Formation
Coalition Mechanics
Coalition Formation Threshold: 50 AE with you
- Nations with 50+ AE can join coalitions against you
- Nations with 30-49 AE are "outraged" but won't join yet
- Nations with <30 AE have normal relations
Coalition Declaration:
- Coalitions form automatically when 4+ nations have 50+ AE
- Coalition grows as more nations reach 50 AE threshold
- Coalition can declare war when they feel strong enough (1.5:1 military strength ratio)
Coalition War Characteristics:
- All coalition members join as co-belligerents
- You fight 5-20+ nations simultaneously
- Extremely difficult to win
- Defeat often means loss of half your territory
AE by Region
Different regions have different AE sensitivities:
High AE Regions (same-culture/religion neighbors)
- Holy Roman Empire (EXTREME - avoid until late game)
- Italy (Catholic nations watch each other closely)
- Iberia (Castile/Aragon/Portugal mutual AE)
- German states outside HRE
Medium AE Regions
- France and neighbors
- Britain and Ireland
- Eastern Europe (Poland, Lithuania, Hungary)
- Anatolia and Middle East
Low AE Regions
- Asia (distant from European politics)
- Africa (less interconnected)
- Americas (colonial expansion generates minimal AE)
Managing AE: Strategic Approaches
Strategy 1: Slow and Steady
Approach: Never exceed 30 AE with any nation
Method:
- Take 1-3 provinces per war
- Wait 10-15 years between wars
- Rotate targets (different regions)
- Allow AE to decay fully
Pros: Zero coalition risk, stable expansion, predictable growth
Cons: Very slow, opportunity cost, boring gameplay
Best For: Beginners, cautious players
Strategy 2: Calculated Aggression
Approach: Expand quickly but stay just below coalition threshold
Method:
- Keep AE at 40-49 (below 50 coalition threshold)
- Use AE-reducing mechanics (see below)
- Rotate expansion between regions
- Time wars for maximum AE decay
Pros: Faster than slow approach, manageable risk, efficient expansion
Cons: Requires careful monitoring, one mistake can trigger coalition
Best For: Experienced players, optimal expansion
Strategy 3: Overwhelming Force
Approach: Ignore AE, become so strong coalitions can't win
Method:
- Expand rapidly in first 50 years
- Build massive military (150%+ force limit)
- Deter coalitions through strength
- Accept coalition wars and win them
Pros: Fastest expansion, domination gameplay, high risk, high reward
Cons: Extremely expensive military, coalition wars are still difficult
Best For: Expert players, major powers (France, Ottomans)
Strategy 4: Colonial Focus
Approach: Expand in low-AE regions (colonies, distant lands)
Method:
- Avoid European wars entirely
- Colonize Americas, Africa, Asia
- Expand through vassals and subjects
- Only fight European wars when necessary
Pros: Minimal AE issues, stable expansion, wealthy trade empire
Cons: Slow European power growth, vulnerable to European rivals
Best For: Portugal, Castile, England
AE-Reducing Mechanics
Reconquest CB (Casus Belli)
Effect: -50% AE on reconquered provinces
How: Vassalize a nation with cores, then reconquer their cores
Example: Vassalize Byzantium → reconquer Greek cores from Ottomans (half AE)
Best Targets: Byzantium, Syria, Persia, Delhi
Return Core CB
Effect: -90% AE when returning cores to their original owner
How: Take land, then return it to the original nation (now your ally/vassal)
Limitation: Requires the original nation to still exist
Use Case: Helping allies/vassals recover their land
Claiming Throne CB
Effect: -25% AE on all conquests in the war
How: Royal marriage with same-dynasty nation → claim their throne
Requirement: Monarchy government, royal marriages
Best For: Monarchies with strong dynastic game
No-CB Wars (Avoid!)
Effect: +100% AE (DOUBLES all AE)
When: Declaring war without valid casus belli
Penalty: Massive AE, stability loss, diplomatic reputation hit
Co-Belligerents
Effect: Spread AE among multiple targets
How: Add enemy allies as co-belligerents in war declaration
Benefit: Taking land from co-belligerent generates less AE
Strategy: If enemy has allies, add them as co-belligerents
Releasing Nations
Effect: Converting conquered land into subjects generates less AE than direct annexation
How: Take land in war → release as vassal → lower AE
Benefit: -25% AE compared to direct annexation
Drawback: Must integrate vassal later (costs time/gold)
Coalition Prevention
Monitoring AE
Check Regularly:
- Diplomacy Panel → Aggressive Expansion tab
- Sort nations by AE with you
- Identify nations approaching 50 AE
Warning Levels:
- 0-29 AE: Safe (green)
- 30-39 AE: Caution (yellow) - slow down expansion in this region
- 40-49 AE: Danger (orange) - stop expanding immediately, improve relations
- 50+ AE: Coalition Risk (red) - they can join coalitions
Improving Relations
Effect: -1 AE per year with that nation (while improving)
Cost: 1 diplomatic action slot
Duration: Until relations reach +100 or you cancel
Strategy: Improve relations with nations at 40+ AE to accelerate decay
Prioritize: Improve relations with:
- Nations at 45-49 AE (prevent coalition join)
- Great Powers (most threatening coalition members)
- Neighbors (most affected by your expansion)
Diplomatic Actions to Reduce AE
- Send Gift: -5 to -10 AE (one-time, expensive)
- Royal Marriage: +25 relations, slight AE decay bonus
- Alliance: Allies cannot join coalitions against you (extremely valuable)
- Guarantee Independence: +10 relations, slight AE improvement
- Trade Agreement: +10 relations
Truce Breaking (Avoid!)
Penalty: Truce breaking generates +50% AE and -5 stability
When: Attacking a nation you have truce with
Dealing with Coalitions
If Coalition Forms
Don't Panic: Coalition formation doesn't mean war immediately
Assessment:
- Check coalition military strength vs. yours
- If you're stronger (1.5:1 or better), coalition won't attack
- If coalition is stronger, prepare defensive strategy
Preventing Coalition War
Option 1: Build Military
- Increase army size to 150%+ force limit
- Build forts on borders
- Station armies defensively
- Deter coalition through strength
Option 2: Ally Out
- Secure powerful allies (France, Ottomans, etc.)
- Allied strength adds to yours for coalition calculations
- Coalition less likely to attack if you have strong allies
Option 3: Wait It Out
- Stop all expansion
- Improve relations with coalition members
- Wait 10-20 years for AE to decay
- Coalition dissolves when members drop below 50 AE
Option 4: Break Coalition
- Ally 1-2 coalition members (removes them from coalition)
- Improve relations with weakest members
- Split coalition diplomatically
Fighting Coalition Wars
If coalition war is unavoidable:
Defensive Strategy:
- Don't Expand Front: Fight defensive battles only
- Use Forts: Forts force coalition to siege (buys time)
- Defeat in Detail: Fight coalition members separately, don't face combined armies
- Naval Superiority: Control seas to prevent reinforcements
- White Peace: Aim for white peace (no gains/losses) or minimal concessions
Peace Strategy:
- Accept white peace if offered
- Give up recently conquered provinces (low integration = low loss)
- Never give up core territories
- Pay gold if needed to end war quickly
Post-War:
- Stop all expansion for 20-30 years
- Rebuild military
- Improve relations extensively
- Wait for AE to fully decay before expanding again
Region-Specific AE Management
Holy Roman Empire (HRE)
AE Multiplier: 2x to 3x normal (EXTREME)
Strategy:
- Avoid HRE expansion until late game (Age of Absolutism+)
- If you must expand in HRE, take 1 province per war maximum
- Better: Dismantle HRE through specific mechanics (advanced strategy)
- Alternative: Become HRE Emperor (grants AE reduction)
Best Approach: Ignore HRE entirely, expand elsewhere
Italy
AE Multiplier: 1.5x (Italian states watch each other closely)
Strategy:
- Expand slowly (1-2 provinces per war)
- Ally some Italian states to prevent coalition
- Focus on wealthy cities (Venice, Milan, Florence) for efficiency
- Use reconquest CB if playing as minor Italian state
Iberia
AE Multiplier: 1.5x (Castile/Aragon/Portugal close ties)
Strategy:
- As Castile: Vassalize/Integrate Aragon through Iberian Wedding event (no AE)
- As Portugal: Focus on colonial expansion (minimal AE)
- Avoid Iberian infighting; expand into North Africa/Americas instead
Eastern Europe
AE Multiplier: 1x (normal)
Strategy:
- More forgiving than Western Europe
- Can expand at moderate pace (2-4 provinces per war)
- Watch for Commonwealth formation (Poland + Lithuania = powerful coalition member)
Anatolia/Middle East
AE Multiplier: 1x (normal), reduced with different religion
Strategy:
- Religious difference reduces AE by ~30%
- Can expand faster than in Europe
- Watch Mamluks and Ottomans (most likely coalition leaders)
Asia
AE Multiplier: 0.8x (distant from European politics)
Strategy:
- European nations care less about Asian expansion
- Ming and regional powers still generate AE
- Fastest expansion region for European nations
Africa
AE Multiplier: 0.8x (fragmented politics)
Strategy:
- Colonial expansion generates minimal AE
- Mamluks and Ottomans are main AE concerns in North Africa
- Sub-Saharan Africa: virtually no AE concerns
Americas
AE Multiplier: 0.5x (colonial regions)
Strategy:
- Conquering native nations: minimal AE
- Conquering colonial nations: moderate AE (only with colonial overlord)
- Best region for fast expansion with minimal consequences
Advanced AE Tactics
AE Rotation
Concept: Rotate expansion between different regions to avoid AE stacking
Method:
- War 1: Expand east (generates AE with eastern neighbors)
- War 2: Expand west (generates AE with western neighbors)
- War 3: Expand south (generates AE with southern neighbors)
- Return to War 4 east (first war's AE has decayed)
Benefit: AE decays in one region while you expand in another
Vassal Feeding
Concept: Your vassals can expand without generating AE for you
Method: Conquer land in war → Transfer conquered provinces to vassal in peace deal
Limitation: Vassal's AE still affects your stability (but less than direct annexation)
Best For: Large-scale expansion without triggering coalitions
Strategic Truces
Concept: 15-year truces prevent coalition wars with truce partners
Method:
- Make white peace or small concessions to key coalition members
- 15-year truce prevents them from attacking in coalition
- Use truce time to reduce AE below 50
Strategy: If coalition forms, declare war on 1-2 strongest members, then white peace
Timing Wars for Maximum Decay
Concept: Time wars to maximize AE decay between conquests
Method:
- Wait 5-10 years between wars (significant AE decay)
- Expand immediately after previous AE has decayed to 20-30
- Maximize expansion per war to minimize total war count
Math: 2 big wars (40 AE each) > 4 small wars (25 AE each)
Common Mistakes
- Expanding Too Fast Early: First 50 years are critical. Slow expansion here prevents late-game coalitions.
- Ignoring AE Until 50: By the time nations hit 50 AE, it's too late. Monitor at 30-40 AE.
- Not Using Reconquest CB: Reconquest is -50% AE. Always vassalize nations with cores before conquering their regions.
- Fighting in HRE: HRE generates 2-3x AE. Avoid completely unless you're an expert.
- Taking High-Development Cities First: Cities generate massive AE. Take rural provinces first, cities later.
- Not Improving Relations: Improving relations actively reduces AE. Use it on high-AE nations.
- Forgetting Distance Modifier: Distant nations care less. Expand away from your core region first.
Quick Reference
- Coalition Threshold: 50 AE
- Safe Expansion Zone: Keep all nations below 40 AE
- AE Decay Rate: 2-4 per year (base)
- Improve Relations Bonus: +1 AE decay per year (per nation)
AE Reduction Methods:
- Reconquest CB: -50% AE (BEST)
- Return Core CB: -90% AE
- Claiming Throne CB: -25% AE
- Co-belligerents: -20% to -30% AE
- Vassal feeding: -30% to -40% AE
High-Risk Regions: HRE (avoid), Italy (caution), Iberia (caution)
Low-Risk Regions: Americas (safe), Africa (safe), Asia (moderate)
Coalition War Strategy: Defensive, use forts, white peace
Prevention: Improve relations with 40+ AE nations, ally powerful neighbors