What are two main causes of the bitter rivalry between the ottoman and safavid empires?

The Ottomans and Safavids have fought each other mainly because the Ottomans were Sunni Muslim and the Safavids were Shiite Muslim. They also fought each other because expanding borders is part of what sustains the economy of these two empires. As a result of conflict between these two empires, each empire's economy was depleted because it spent so much on wars that ended up not helping the empire in any way. This partially contributed to the decline of these two empires.