Diplomatic Relations

Relations between civilizations are bit flags in int treaties[8][8] (GLOBALS.C). treaties[a][b] describes how civilization a regards b. Contact and peace are always set and cleared in both directions; most other bits are one-sided.

Row 0 is used differently. Bit 0x004 of treaties[civ][0] marks a government that has collapsed into anarchy; city_phase() and set_government() in DIPLOMAC.C use it to time the revolution and its announcement.

Contact and the sixteen-turn period

When units of two civilizations meet, UNITS.C calls diplomacy_event(), which sets 0x011 in both directions. If the human is one of the pair, a first contact, or a meeting at least sixteen turns after the last audience, opens a leader audience.

Every sixteenth turn, city_phase() checks each pair. A pair without 0x010 loses contact; if it was at war, a civilization with whom the human has an embassy reports “The war between … has ended.” The 0x010 bits are then cleared for the next period. War therefore lapses after sixteen turns without contact.

Setting and breaking peace

Two helpers in DIPLOMAC.C change the relationship in both directions:

• relation_set(a, b, 2) signs peace, posts a replay event and clears the fighting bits.
• accord(a, b, 2) cancels peace. It posts a replay event when a treaty existed and also clears the alliance bit.

BATTLE.C sets 0x020 in both directions after every combat. If the two civilizations were at peace, it reports “… cancel peace treaty with …” and calls accord(). When the human is the attacker, the victim also records a grievance (0x008). Before an attack, attack_ok() asks the human to confirm breaking a treaty; under a Republic or Democracy the Senate refuses.

Grievances

0x008 makes an AI less forgiving: it greets the human with “O most untrustworthy leader of the infidels” and doubles the tribute it demands. The bit is set when:

• the human attacks a civilization at peace with it;
• the human agrees to an AI’s request to cancel a treaty with a third civilization, or joins an AI’s war against one (the third civilization records the grievance);
• a nuclear weapon strikes the civilization (atom() sets 0x088);
• a civil war creates a new civilization (treaties[new][old] |= 9).

set_government() clears all of a civilization’s grievances when its government changes.

Planned cancellation and sneak attacks

An AI at peace with the human that is hostile in an audience, but weaker than the human or holding a grievance, makes no demand. It sets 0x100 instead, deciding to end the treaty later. On each later turn, city_phase() has a one-in-three chance of clearing 0x100 and peace and setting 0x200. The next battle in which that civilization attacks is announced as “Sneak attack by … forces!”, and the bit is cleared. The same message appears whenever a civilization attacks the human while the human still regards it as at peace. unit_phase() treats a civilization with 0x100 set as an enemy when it plans its continents.

Embassies

Bit 0x040 in treaties[civnow][civ] gives the human intelligence about civ. A Diplomat sets it (DIPLOMAT.C). It enables the “Check Intelligence” option when an emissary arrives, the dossier in the foreign affairs report, and messages about that civilization’s discoveries, wars, treaties and conquests.

give_advance() in ECONOMY.C was meant to exchange ambassadors automatically at Chieftain level when a rival learns Writing. Its test is (!treaties[civnow][civ] & 0x40): ! binds first and yields 0 or 1, so the test is always false. The recovered source keeps that expression because the original binary contains it.