Answer:
The conflict has its roots in the failure of a political transition supposed to bring stability to Yemen following an Arab Spring uprising that forced its longtime authoritarian president, Ali Abdullah Saleh, to hand over power to his deputy, Abdrabbuh Mansour Hadi, in 2011.
Explanation:
While it could be from literally anywhere, I'd assume most of them came from the Soviet Union, Germany, France, and Poland, along with plenty of other smaller countries like Austria, Hungary, and even Greece.
