Complex sentence: The French became responsible for Syria and Lebanon, while the British were given mandates for Mesopotamia and Palestine, with this process eventually leading to the formation of the modern states of Turkey, Iraq, Israel, Jordan, Lebanon, and Syria.
Split into simpler sentences: The French became responsible for Syria and Lebanon, while the British were given mandates for Mesopotamia and Palestine. Which eventually led to the formation of the modern states of Turkey, Iraq, Israel, Jordan, Lebanon, and Syria.