What Matters
Relations, trust, rivals, subjects, and aggressive expansion are the core diplomatic mechanics. Fewer enemies early means fewer cascading wars. Understanding these systems helps you build stable alliances and avoid costly conflicts.
Tip
Key principle: A stable diplomatic foundation prevents costly defensive wars and opens opportunities for expansion.
Opening Routine
Establish your diplomatic foundation in the first 20 years:
- One neighbor ally of similar weight: Find a neighbor with similar power and interests. This deters early aggression and provides military support.
- Improve relations with trade partners: Boost relations with nations you trade with. Positive relations improve trade deals and reduce conflict risk.
- Pick one local rival for projection: Choose one nearby rival to focus your diplomatic efforts. Don't rival distant great powers—they're not immediate threats.
Tip
Early focus: Build one strong alliance and improve relations with key trade partners. Avoid spreading your diplomatic efforts too thin.
Subject Play
Vassalization is a powerful tool for expanding without direct administrative burden:
- Vassalize soft neighbors: Target weaker neighbors that can be vassalized through diplomacy or short wars. They provide manpower and income without full integration costs.
- Integrate when economy can absorb costs: Only integrate vassals when your economy can handle the additional administrative burden and control loss.
- Use subjects for buffer zones: Vassals can act as buffer zones against stronger neighbors, reducing direct threats to your core territory.
Tip
Integration timing: Integrate vassals when you have stable economy and sufficient administrative capacity. Don't rush integration—vassals provide value even without integration.
Coalition Avoidance
Aggressive expansion (AE) triggers coalitions when you expand too quickly:
- Pace conquests: Don't take too much land in a single war. Spread conquests over multiple wars to let AE decay.
- Mix diplomatic gains with economic growth: Balance military expansion with diplomatic and economic development. Not every war needs to be about territory.
- Keep AE below thresholds in dense regions: In regions with many small states (like the Holy Roman Empire), be especially careful about AE. Coalitions form faster in dense regions.
- Improve relations with potential coalition members: Positive relations reduce the chance of joining coalitions. Keep relations high with neighbors you might expand into.
Coalition warning: If you see a coalition forming, improve relations immediately or wait for AE to decay before continuing expansion.
Patch Angle (v1.0.x)
EU5's new systems make diplomacy more context-aware:
- Politics/estates and populations make AI more context-aware: The AI considers internal politics, estate balance, and population needs when making diplomatic decisions.
- Stable internal politics improve deal-making: Nations with stable internal politics (good estate balance, satisfied populations) are more reliable partners and easier to negotiate with.
- Situations affect diplomatic options: Time-bound situations can create diplomatic opportunities or pressures. Use them to your advantage.
Note
EU5 difference: Internal stability now directly affects your diplomatic standing. Manage your estates and populations to improve your diplomatic position.
First 20 Years Checklist
- Secure one strong neighbor ally to deter early aggression
- Improve relations with key trade partners and potential vassals
- Pick one local rival for focused diplomatic projection
- Consider vassalization of weak neighbors for buffer zones
- Monitor aggressive expansion and pace conquests accordingly
- Maintain stable internal politics to improve diplomatic standing