Russia is bombarding Aleppo because Putin wants a navy base in the Mediterranean, and his ticket to that is to keep Assad in power in Damascus no matter the cost. There are moderate rebels striving for a modern state, there are islamic extremist rebels, and there are some ethnic Turks and Kurds. This comes on top of the previous conflict in Iraq with Sunnis, Shias, and Kurds fighting each other, each with their links to kinfolks in other countries in the region.
The most problematic of these circumstances is the Kurdish case. It is the largest ethnic group in the world that does not have a country, a nation state. Their land is split between four countries, Turkey, Iran, Iraq, and Syria. Turkey is helping the moderate rebels in Syria against Assad but their main foe is the Kurds. Apparently the situation is as follows:
Russia's enemies: 1) moderate rebels, Kurds; 2) ISIS. Friends: Assad. Turkey's enemies: 1) Kurds; 2) Assad; 3) ISIS. Friends: Moderate rebels. USA's enemies: 1) ISIS; 2) Assad. Friends: Moderate rebels, Kurds.
There is one factor and one factor only that prevents the West from showing a united front, and it is the Kurdish problem. The fact that Turkey is insisting on subjugating a large tract of Kurdish land.
Turkey would have a lot to win on reconsidering its stance on Kurdistan. They would get more stability, and stability leads to economical development. It could also open the doors for EU membership. Furthermore, it would give them a friendly eastern neighbor that can act as a buffer to Iran, a very useful buffer since there are Kurds on the other side of the border as well, inside Iran. A Kurdistan created with pieces from present Iraq and Turkey would put Teheran on the defensive. By removing this problem from the table, all efforts could be focused on defeating the bad guys in the Levant (a people wanting sovereignty is not a bad guy!). It seems that it’s in Ankara’s interest to reconsider the Kurdish question.