It's Iran who placed Al Maliki with US support. I've heard specialits talking about it but you can see a Shia saying it himself :
Al Maliki have let ISIS enter easily in Irak, he knew they were coming and he let them done it.
Bashar (supported by Iran)also let many terrorists and criminals out of prisons, like did Ben Ali during the revolution and same in Libya.
In case you haven't noticed it's always the same tactic made by arab leaders : they let terrorists spread destruction and fear the people , then act like heroes and like they are the only way : so dictatorship or extremists
Made by Algeria, Egypt, Tunisia, Syria etc ...
In Yemen what's happening is that the country is not united, some years ago it was split in 2 parts like North and South Korea and if i remember well they had then 2 presidents. Also they have some problems with Saudi Arabia in the borders since a long time and as they are many tribes and the governement is corrupted then everyone is making his own law.
Now Iran try to take an advantage with the Houthis by helping them talking the power.
All those influences game between Sunni and Shias here and there creates injustice and then extremists.
When one have the power, he is supported by this or that regime and the people who have not the "right" sect at this moment are left appart.