What political system did European countries set up that caused conflicts in the Middle East?

As the Ottoman Empire collapsed and disintegrated into nations with indistinct borders and decentralized government, the United Kingdom and France occupied the territories which were left behind. Look at this photo:

Source: https://www.vox.com/a/maps-explain-the-middle-east

Most of the conflict in the middle east in the modern world is in this region, where Iraq, Iran, Lebanon, Jordan, Israel, Iran and Palestine(not a nation yet) exist. As the British and French occupies these regions, they didn't really care about how there was religious division and all this ethnic conflict. But as the years passed, and throughout World War II, they've realized the dangers within the regions and how it was reminiscent of the Balkans. In order to maintain order, stability and control in the region, they've decided to cut up these nations into independent states. But they were missing one aspect - religion.

For example take a look at modern Israel and Palestine. Not a distinct state was established, and the confusion caused by the UN ratification of the establishment of Israel, the Six-Day and Yom-Kippur War made it hard to decide which distinct region is occupied by Israel or Palestine. Also look at the Kurds, which have no distinct state, but are inhibiting in the borders of Turkey, Syria and Iraq. Assyrians make a minority, but are also engrained in the Syrian borders.

This is where the lack of establishing a distinct state causes chaos. The current conflict in Syria-Iraq is one of the most known conflict beside the civil war in Yemen or the border dispute in Israel. The conflict between Sunni and Shia Muslims as well as the ethnic groups within are caused by the failures of the European nations.