Why didn't Obama get more involved in the never ending Sunni versus Shia war?

Because it is a completely no-win situation for everyone. If you go back and study the

1. The 30 Years War: Catholics vs. Protestants -...

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   The 30 Years War: Catholics vs. Protestants. ... Christian IV, Denmark's Protestant king, felt Ferdinand II was a threat to Protestants everywhere. In 1625, ... 

   
   

   in Christianity you get some idea of just how insane all this is and is going to get in the Middle East and elsewhere before it is all over sometime 25 to 200 years from now.

   
   

   So, Obama really doesn't want to completely side with Shias (because of Russia) or Sunnis because of Saudi Arabia and Turkey and Jordan and all the rest of the Sunni Ruled nations.

   
   

   In other words as the ONLY real Superpower left (unless you consider China as a superpower) it is a completely no win situation for a Christian nation like the U.S. to get too involved in either side of the  Sunni versus Shia war that spills over as terrorism into Europe and the U.S. and all over the world as well. 

   
   

   However, my thought is that Iran and Saudi Arabia either already have nuclear weapons or will soon and possibly Turkey too at this point.

   
   

   So, at some point just expect these nukes to be used in frustration against each other in reality on the ground.

   
   

   Though traditionally Saudi Arabia and Turkey (Should) be on the same side of all this, it is debatable how all this is all going to go in reality because Turkey doesn't have regular army units on the ground fighting anywhere except guarding Turkish borders for now.

   
   

   But, Saudi Arabia is fighting a proxy war in Yemen against Iran who funds the Houthi Shia warriors there.

   
   

   So, it is all a complete mess and getting worse every day.

   
   

   The latest problem is Aleppo and the 2 million starving thirsty Sunni Muslims who might die of starvation or thirst in the latest siege against them by Assad and Russia and Hezbollah and Iran.