diff --git a/app/game-engine/test/npcNationWarDeclaration.test.ts b/app/game-engine/test/npcNationWarDeclaration.test.ts
new file mode 100644
index 0000000..6ac0dd9
--- /dev/null
+++ b/app/game-engine/test/npcNationWarDeclaration.test.ts
@@ -0,0 +1,238 @@
+import { describe, expect, it } from 'vitest';
+import type { TurnSchedule, UnitSetDefinition } from '@sammo-ts/logic';
+import type { InMemoryTurnWorld } from '../src/turn/inMemoryWorld.js';
+import type { TurnGeneral, TurnWorldSnapshot, TurnWorldState } from '../src/turn/types.js';
+import { LARGE_TEST_MAP, buildLargeTestCities } from './fixtures/largeTestMap.js';
+import { createTurnTestHarness, createWorldDebugger } from './helpers/turnTestHarness.js';
+
+const mockDate = new Date('0183-05-01T00:00:00Z');
+
+const createNpcGeneral = (
+    id: number,
+    cityId: number,
+    nationId: number,
+    officerLevel: number,
+    stats: { leadership: number; strength: number; intelligence: number }
+): TurnGeneral => ({
+    id,
+    name: `NPC_${id}`,
+    nationId,
+    cityId,
+    troopId: 0,
+    stats,
+    turnTime: mockDate,
+    role: {
+        items: { horse: null, weapon: null, book: null, item: null },
+        personality: null,
+        specialDomestic: null,
+        specialWar: null,
+    },
+    triggerState: { flags: {}, counters: {}, modifiers: {}, meta: {} },
+    meta: {},
+    officerLevel,
+    experience: 0,
+    dedication: 0,
+    injury: 0,
+    gold: 20000,
+    rice: 20000,
+    crew: 0,
+    crewTypeId: 0,
+    train: 0,
+    atmos: 0,
+    age: 30,
+    npcState: 2,
+});
+
+const maxCityStats = (city: ReturnType<typeof buildLargeTestCities>[number]) => ({
+    ...city,
+    population: city.populationMax,
+    agriculture: city.agricultureMax,
+    commerce: city.commerceMax,
+    security: city.securityMax,
+    defence: city.defenceMax,
+    wall: city.wallMax,
+    meta: { ...(city.meta ?? {}), trust: 100, trade: 100 },
+});
+
+describe('NPC 선전포고 조건 테스트', () => {
+    it('183년 5월 시작 후 3개월 이내 선전포고가 발생해야 한다', async () => {
+        const cities = buildLargeTestCities().map(maxCityStats);
+        const cityA1 = cities.find((city) => city.id === 1)!;
+        const cityA2 = cities.find((city) => city.id === 2)!;
+        const cityB1 = cities.find((city) => city.id === 3)!;
+        const cityB2 = cities.find((city) => city.id === 5)!;
+
+        cityA1.nationId = 1;
+        cityA2.nationId = 1;
+        cityB1.nationId = 2;
+        cityB2.nationId = 2;
+
+        const unitSet: UnitSetDefinition = {
+            id: 'test_unit_set',
+            name: 'TestUnitSet',
+            defaultCrewTypeId: 1100,
+            crewTypes: [
+                {
+                    id: 1100,
+                    armType: 1,
+                    name: '보병',
+                    attack: 10,
+                    defence: 10,
+                    speed: 10,
+                    avoid: 0,
+                    magicCoef: 0,
+                    cost: 10,
+                    rice: 1,
+                    requirements: [],
+                    attackCoef: {},
+                    defenceCoef: {},
+                    info: [],
+                    initSkillTrigger: null,
+                    phaseSkillTrigger: null,
+                    iActionList: null,
+                },
+            ],
+        };
+
+        const generals: TurnGeneral[] = [];
+        let nextId = 1;
+        const pushNationGenerals = (nationId: number, cityId: number) => {
+            generals.push(createNpcGeneral(nextId++, cityId, nationId, 12, {
+                leadership: 90,
+                strength: 80,
+                intelligence: 40,
+            }));
+            for (let i = 0; i < 9; i += 1) {
+                generals.push(createNpcGeneral(nextId++, cityId, nationId, 2, {
+                    leadership: 70,
+                    strength: 80,
+                    intelligence: 30,
+                }));
+            }
+            for (let i = 0; i < 10; i += 1) {
+                generals.push(createNpcGeneral(nextId++, cityId, nationId, 2, {
+                    leadership: 70,
+                    strength: 30,
+                    intelligence: 80,
+                }));
+            }
+        };
+        pushNationGenerals(1, cityA1.id);
+        pushNationGenerals(2, cityB1.id);
+
+        const snapshot: TurnWorldSnapshot = {
+            generals: generals as any,
+            cities: cities as any,
+            nations: [
+                {
+                    id: 1,
+                    name: 'NPC_A',
+                    color: '#AA0000',
+                    capitalCityId: cityA1.id,
+                    chiefGeneralId: 1,
+                    gold: 1000000,
+                    rice: 1000000,
+                    power: 0,
+                    level: 1,
+                    typeCode: 'npc',
+                    meta: { tech: 0 },
+                },
+                {
+                    id: 2,
+                    name: 'NPC_B',
+                    color: '#0000AA',
+                    capitalCityId: cityB1.id,
+                    chiefGeneralId: 21,
+                    gold: 1000000,
+                    rice: 1000000,
+                    power: 0,
+                    level: 1,
+                    typeCode: 'npc',
+                    meta: { tech: 0 },
+                },
+            ],
+            troops: [],
+            diplomacy: [],
+            events: [],
+            initialEvents: [],
+            map: LARGE_TEST_MAP as any,
+            scenarioConfig: {
+                stat: { total: 300, min: 10, max: 100, npcTotal: 150, npcMax: 50, npcMin: 10, chiefMin: 70 },
+                iconPath: '',
+                map: {},
+                const: {
+                    openingPartYear: 3,
+                    develCost: 10,
+                    baseGold: 1000,
+                    baseRice: 1000,
+                    maxResourceActionAmount: 10000,
+                    minAvailableRecruitPop: 0,
+                },
+                environment: { mapName: 'large_test_map', unitSet: 'default' },
+            },
+            scenarioMeta: {
+                startYear: 180,
+            } as any,
+            unitSet: unitSet as any,
+        };
+
+        const state: TurnWorldState = {
+            id: 1,
+            currentYear: 183,
+            currentMonth: 5,
+            tickSeconds: 600,
+            lastTurnTime: mockDate,
+            meta: { seed: 1, initYear: 183, initMonth: 5 },
+        };
+
+        const schedule: TurnSchedule = {
+            entries: [{ startMinute: 0, tickMinutes: 10 }],
+        };
+
+        const worldRef = { current: null as InMemoryTurnWorld | null };
+        let declaredAt: { year: number; month: number; nationId: number } | null = null;
+
+        const { runUntil } = await createTurnTestHarness({
+            snapshot,
+            state,
+            schedule,
+            map: LARGE_TEST_MAP,
+            worldRef,
+            onActionResolved: (payload) => {
+                if (payload.kind !== 'nation') {
+                    return;
+                }
+                if (payload.actionKey !== 'che_선전포고') {
+                    return;
+                }
+                const world = worldRef.current;
+                if (!world || declaredAt) {
+                    return;
+                }
+                const { currentYear, currentMonth } = world.getState();
+                declaredAt = { year: currentYear, month: currentMonth, nationId: payload.nationId ?? 0 };
+            },
+        });
+
+        const debug = createWorldDebugger(() => worldRef.current, {
+            nationIds: [1, 2],
+            cityIds: [cityA1.id, cityA2.id, cityB1.id, cityB2.id],
+            includeNationSummary: true,
+        });
+
+        try {
+            await runUntil(
+                (current) => current.currentYear > 183 || (current.currentYear === 183 && current.currentMonth >= 8)
+            );
+        } catch (error) {
+            debug.dumpWatched('선전포고 테스트 실패');
+            throw error;
+        }
+
+        if (!declaredAt) {
+            debug.dumpWatched('선전포고 미발생');
+        }
+
+        expect(declaredAt).not.toBeNull();
+    });
+});