Summary
Iran has played a pivotal role in Syrian President Bashar Assad's campaign to crush rebel resistance in Aleppo.
Thousands of Shiite militia fighters trained by Iran are fighting on the side of the government in Iraq.
Some have already fought in Syria to support Assad and pledged to go back if necessary.
Iran already has a great deal of influence in Lebanon, where it has deep historical ties with the Shiite community and funds Hezbollah, the country's most powerful political and military movement, which is also fighting in Syria on behalf of Assad.
That decision to keep senior Iranian commanders at the front line came at a cost, with at least half a dozen Iranian generals killed in Syria. But by using Shiite militia fighters from other countries, Tehran was able to keep the total number of Iranians killed in Syria relatively low.
Earlier this year, Khamenei said that if Iran was not taking part in the war in Syria then they would be fighting the same enemy inside Iran.
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