The U.S. just cut $900 million in security aid to Pakistan. Here's why.

The White House suspended payment of at least $900 million in security aid to Pakistan Thursday, demanding its government take action against two terror groups using Pakistan as a staging post for raids into Afghanistan.

“We will not be delivering military equipment or transfer security-related funds to Pakistan unless it is required by law,” said State Department spokeswoman Heather Nauert.

U.S. President Donald Trump previewed the policy in a tweet on New Year’s Day:

The U.S. wants to spur Islamabad into taking concrete steps to curb terrorism. “We’re hoping that Pakistan will see this as an incentive, not a punishment,” a State Department official told Reuters.

Why is the US so angry with Pakistan?

The White House thinks Islamabad is not doing enough to fight terrorism. Specifically, the U.S. wants Pakistan to deal with the Afghan Taliban and Haqqani network militant groups, which use Pakistani territory to launch attacks in neighboring Afghanistan, killing U.S., Afghan, and other forces.

Why shouldn’t Pakistan be surprised?

The Trump administration has been pushing Pakistan for some time to change its approach. The first sign came in August when the White House announced it was putting aside $255 million in military assistance, which Pakistan could only access if it clamped down on internal terror groups.

Secretary of State Rex Tillerson and Secretary of Defense James Mattis have in recent months visited Islamabad to push for more action.

“Pakistan must demonstrate its desire to partner with us,” Tillerson wrote last week in a New York Times op-ed.

U.S. ambassador to the U.N., Nikki Haley, said Tuesday Pakistan “has played a double game for years [and] that game is not acceptable to this administration.”

The State Department also announced Thursday that Pakistan was being added to a special watch list for "severe violations of religious freedoms.”

What will Pakistan do?

Islamabad has long denied it helps militants within its borders and has shrugged off U.S. threats to cut aid. However, the government will be wary of further economic sanctions from Washington.

But the move could also backfire.

Former Defense Secretary Leon Panetta told CNN that pushing Islamabad too hard on this could drive it closer to Russia and China, which have both sought closer ties with Pakistan.

Pakistan could also shut down land and air routes into Afghanistan, which the U.S. relies upon to supply its troops.