There are lots of countries whose borders were imposed by European imperialists that manage to do fine, but the point is that French colonialism set up modern-day Syria in a way that contributed to tension between ethnic and religious groups, which eventually became important for today's war.
One religious minority group, Alawite Shia Muslims, in particular saw French colonialism as an opportunity. Long persecuted as "heretics" by the much larger population of Sunni Muslims, some Alawites joined up with French colonial authorities. In particular, they joined the newly constructed Syrian military — a development the French welcomed as a means of cementing their power. European colonialists often promoted minority groups that would rely on them to maintain power, so the relationship was symbiotic.
The French eventually left, but the borders stayed. In 1963, the Syrian military took power, and the government quickly became dominated by Alawites
When Hafez al-Assad came to power in 1970, virtually all the top power brokers in Syria were Alawites," Glenn Robinson, an associate professor at the Naval Postgraduate School, writes.
This created a dangerously precarious political situation. The Alawites saw (and continue to see) maintaining a sectarian government as their best hope for securing themselves from persecution and even massacre. But the Sunni majority was blocked from meaningful political power and angry about it. This could only last for so long.
