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Since the flags were spotted in Kurd-controlled territory last week, Turks and Kurds have squabbled about their origins.
Turkey's push into Syria is a major escalation in their involvement in the war.
It's Turkey’s first major U.S.-backed incursion into Syria.
The new deployment increases U.S. forces in Syria six-fold to about 300.
WHAT'S HAPPENING
Many fighters have joined anti-Islamic State militias out of a sense of moral duty.
The Kurdish militia regularly coordinates with U.S.-led forces bombing the Islamic State.
The Kurdish militia is among the most effective ground forces against ISIS.