Shari’a prescribed permanent war between Islam and Christendom, in theory only.

Evidence

A second major category is travel related to war: I did at the beginning exclude invasions, expulsions and other military movements, but there is still a certain amount of individual travel related to war and its preparation. In prin­ ciple, there was of course a permanent state of war between Islam and Christen­ dom as laid down by Shari‘a; the one is the Dar al-Islam (House of Islam); the other is the Dar al-Harb (the house of war). Theoretically there could be truces but no permanent peace. In point of fact reasonably peaceful relations were at times maintained between some Christian and some Muslim governments. — Bernard Lewis, From Babel to Dragomans, 746

Categorization

• DEFINE: Defines the Dar al-Islam / Dar al-Harb distinction as it actually operated in travel law.