Complex sentence: A large portion of what was captured was to become the Israeli-controlled portion of Jerusalem- "West Jerusalem"--but some of the heaviest battles of the 1948 Arab-Israeli war were to follow and the Jerusalem frontier was to be redrawn many times.
Split into simpler sentences: A large portion of what was captured was to become the Israeli controlled portion of Jerusalem- "West Jerusalem". But some of the heaviest battles of the 1948 Arab-Israeli war was to follow and the Jerusalem frontier was to be redrawn many times.