What constitutes peace?
Assuming that the enemy declines the initial invitation to escape [battle] but evinces interest in the second invitation - to make peace; How is the surrender effected?
RAMBAM's answer is: By renouncing idolatry and accepting the seven Noahide commandments. (Hilkhot Melakhim 8:9)
Likewise, a city which surrenders, we do not make a [peace] treaty with them until they renounce idolatry, destroy all their places [of worship], and accept the remaining [six] Noahide commandments.
The seven Noahide commandments are, essentially, the laws which are fundamental to the operation of any civilized society. They are so important that a gentile who accepts them, voluntairly (i.e., not in time of war), attains the status of a resident alien, and is entitled to permanent residence in Eretz Yisrael! [NOTES: 1. Some authorities require the acceptance of ALL mitzvot except eating. 2. The question of the "resident alien" status of the Palestinian Arabs, and of other non-Jews in Israel, today, is a most serious and sensitive one.]
And elsewhere (Hilkhot Melakhim 6:1), he elaborates:
If they surrender and accept the seven Noahide commandements, not one of them may be killed. To wit: "They shall be your tributaries and serve you" (Dt. 20:11). If they agree to pay tribute but refuse service; or if they accept the service but refuse to pay tribute - we do not heed them until they consent to both conditions.
The service to which they are subjected consists of being humbled and degraded, showing no definace of Israel, and remaining subdued in their presence. The tribute consists of their preparedness to serve the [Israelite] king physically and monetarily, such as: building walls, strengthening fortifications, constructing the king's palace, etc.
Without getting into all the halakhic complications [e.g., comparing RAMBAM's position with that of the TOSAFOT (Gittin 46a, s.v.), etc.] there seem to be three steps in the peace/surrender process leading, gradually, from the cessation of hostilities to alien residency: (1) renunciation of idolatry; (2) acceptance of the seven Noahide comandments; and (3) paying tribute and remaining subservient to Israel.
Postscript to the Peace Process:
Two further reservations pertain to the peace rpocess, one on each side.
On the Enemy Side, the suit for peace must be genuine, unanimous, and accompanied by peaceful actions. As [our Great Sages] state in their interpretations of Dt. 20:10-13:
If they respond in peace - implies a verbal response. Therefore Scripture adds: ...and they open up before you - in deed, and not just in word.
If they respond in peace - perhaps even only some of them? Therefore Scripture adds: ...and they open up; it must be unanimous.
If it declines to make peace and wages war against you and you besiege it - God will turn it over to you. If you call to it in peace and do everything you're supposed to do, and still they decline - God will eventually turn it over to you.
On Israel's Side, too, the peaceful conclusion of hostilities carries a further moral responsibility:
After they make peace and accept the seven Noahide commandements, it is forbidden to either lie to them or trick them in the conclusion of a treaty.