The White House made an announcement on Sunday that shocked its allies in Syria. President Donald Trump's administration announced that Turkish forces would soon move into portions of northern Syria which are currently controlled by Kurdish groups, and that US troops in the area would step aside.

While the Kurds have been Washington's staunchest and most effective allies in the war against ISIS, it now appears they will be left to Turkey's mercy.

Turkey's military has begun to cross into northern Syria, the Turkish government said early Wednesday, as part of an impending offensive to move Kurdish forces away from its border.

It comes after the Trump administration released a statement saying US forces "will not support or be involved in the (planned Turkish) operation" and that American troops "will no longer be in the immediate area."

As of last month, the US said about 1,000 US troops were operating in northeastern Syria. Sunday's statement did not specify if this constituted a full withdrawal of personnel from the country.

But what's behind Turkey's move to enter northern Syria? What is the potential impact of the US pull-out? And how will it impact the region's security? Here are some answers:

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