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    Diplomacy & Expansion

    Understanding alliances, royal marriages, personal unions, coring mechanics, and smart expansion strategies.

    Core Diplomatic Actions

    Alliances

    Defensive pacts that pull allies into wars

    Benefits: Military backup, coalition deterrent

    Cost: Diplomatic capacity slot, trust management

    Royal Marriages

    Build relations and enable Personal Union claims

    Benefits: Improved relations, PU potential

    Warning: Breaking costs stability and opinion

    Rivals

    Required for efficient expansion (choose 3 neighbors)

    Strategic: Rival nations you plan to attack

    Benefit: Gain prestige from rival defeats

    Claims

    Reduce aggressive expansion and province cost

    Critical: Always use claims CBs when available

    Source: Mission trees, fabricate claims, events

    Diplomatic Capacity Management

    Each alliance, subject, and royal marriage costs diplomatic capacity slots. Don't overcommit early—you'll need capacity for vassals and personal unions later.

    Personal Unions (PU)

    Personal Union Integration Process

    1

    Requires: Royal Marriage + Dynastic Claim

    Establish royal marriage, then wait for claim event or opportunity

    2

    5-Year Wait for Seniority

    Determined by grade power score. Cannot proceed until seniority established.

    3

    Pass 5 Sequential Centralization Laws

    Union Foundation → Codification Inheritance (after 10 years) → Economy of Unions → Administrative Unions → Final integration law (after 50-year wait from seniority)

    4

    Integration Begins

    Only after all 5 laws passed can you begin actual integration. Process takes years depending on subject size.

    Strategic Insight: Shrink Before PU

    Integration time scales with subject size. Smaller nations integrate dramatically faster.

    Example: Castile attacking Portugal pre-union to shrink them from 6 provinces to 3 provinces = integration completes 10+ years faster post-union.

    Coalition Management

    High Aggressive Expansion = Coalition Wars

    When too many nations fear your expansion, they form defensive coalitions. Coalition wars are brutal—the entire coalition attacks simultaneously.

    Use Religious Wars and Claims CBs

    These Casus Belli provide reduced aggressive expansion. Always fabricate claims or use mission tree claims before declaring war.

    Improve Relations with Threatened Nations

    High relations reduce coalition join chance. Assign diplomats to improve relations with nations showing high AE against you.

    Take Breaks Between Major Conquests

    AE decays over time (typically -2 per year). After conquering 3-5 provinces, wait 5-10 years for AE to decay before next major war.

    Monitor Coalition Formation (Diplomacy Tab)

    Check which nations have high AE against you. If 4+ nations show "Outraged" status, coalition risk is high. Pause expansion.

    Province Integration & Coring

    Three-Tier Integration System

    TIER 1Conquered

    • • Assimilation/conversion speed -20%
    • • Maximum control -10%
    • • Separatism +50% (high rebellion risk)

    TIER 2Integrated (Yellow colored)

    • • Assimilation speed -10%
    • • Control +5%
    • • Separatism +10%

    TIER 3Core

    • • Maximum control +20% (full bonuses)
    • • Achieved at ≥50% state religion (no culture requirement!)
    • • Alternatively: ≥50% primary or accepted culture

    Critical Insight: Religious Conversion is Faster

    Religious conversion makes provinces cores quickly (only ≥50% state religion required). Cultural assimilation is slower but permanent.

    Strategic choice: Convert religion for immediate coring, or wait for cultural assimilation for long-term integration. Most players prioritize religious conversion first.

    War Target Selection

    1

    Check Their Allies Before Declaring

    Diplomacy tab → View target nation → Allies. Avoid fighting the entire world. Sometimes a 5K nation is allied to France (50K troops).

    2

    Verify You Have a Valid CB (Casus Belli)

    Claims, religious wars, missions provide CBs with reduced AE. No-CB wars cost massive prestige and maximum AE.

    3

    Ensure You Can Actually WIN

    Compare military strength (visible in war declaration screen). If they + allies have 2x your army size, reconsider or wait for better opportunity.

    4

    Consider Truce Timers

    Can't attack the same nation again for 5-15 years after peace. Plan multi-war conquests accordingly.

    Advanced Diplomacy & Expansion

    Related Topics

    Military Fundamentals

    Learn how to win wars and siege forts

    Read Guide

    Population & Culture

    Understand integration and cultural acceptance

    Read Guide