President Donald Trump declared victory over ISIS on Wednesday and said the only reason for the US having a military presence in Syria was to fight the terror group.

In saying so, Trump threw out about a year of the State Department and Pentagon's explicitly stated policy.

The US withdrawing from Syria will give Russian President Vladimir Putin a freer hand to impose his will on the region, as Russia is now the unopposed military power in the region.

The US has been fighting against ISIS in Syria since 2014, and the terror group is down to a tiny fraction of the territory and strength it started with before the US started bombing it.

President Donald Trump declared victory over ISIS on Wednesday and said the only reason for the US having a military presence in Syria was to fight the terror group.

In saying so, Trump has ignored more than one year of explicit policy from his own top military and State Department officials.

For example, four days before Trump's declaration, which coincided with widespread reports that the US would pull out all troops from Syria, the Pentagon said the following:

"We remain committed to working with our partners on the ground to ensure an enduring defeat of ISIS. Any reports indicating a change in the U.S. position with respect to these efforts is false and designed to sow confusion and chaos."

Business Insider reached out to the Pentagon for comment on Trump's apparent reversal of policy but received no comment.

What the US was doing in Syria

A US Air Force F-22 Raptor flies over the Arabian Sea in support of Operation Inherent Resolve on January 27, 2016. US Air Force photo by Staff Sgt. Corey Hook

The US started military intervention in Syria in 2014 to combat ISIS. This intervention has mostly taken the form of an air campaign with more than 70 nations contributing jets, munitions, or funds to fight the terror army.

Read more: One photo shows the incredible firepower of the US-led coalition against ISIS

The US, Israel, and others accuse Iran of trying to ally themselves with Syrian President Bashar Assad to secure freedom of movement in the country and thereby facilitate arms transfers to Lebanon, where Hezbollah holds considerable military and political power — and shares Iran's dream of destroying Israel.

In September, former US Ambassador James Jeffrey, now the State Department's representative for Syrian engagement, said the US was in no hurry to leave Syria and could stay behind after the defeat of ISIS to counter Iran.

More explicitly, national security adviser John Bolton said US troops are not leaving Syria "as long as Iranian troops are outside Iranian borders."

Trump has taken a hawkish line against Iran and was thought to have picked Bolton and Secretary of State Mike Pompeo precisely because they shared his goal of countering Iran's vision.

But on Wednesday Trump threw months of US policy away and declared the US' sole reason for having boots on the ground in Syria was to fight ISIS.

Big win for Putin

Russia announced it will pull most of its troops from Syria starting March 15, in a process that could take up to five months. Ministry of Defence of the Russian Federation

Russia sent warplanes to back Assad in Syria at the end of September 2015. Russia's jets turned the tide of the war and saved Assad from near certain defeat at the hands of rebels.

In November 2017, with Assad firmly back in control of Syria and crushing the remaining pockets of rebel fighters with the help of Russian air power, the Syrian leader gave Russian President Vladimir Putin a big hug and thanked him for his help.

Putin filled a power vacuum left in Syria after former President Barack Obama refused to do any more than train and equip rebel groups in Syria. The US at the time had few, if any, troops in Syria.

But Trump, by sending forces into Syria, was able to thwart many of Putin's ambitions. US forces on the ground clashed with Russian military contractors in a huge battle that left many slaughtered and humiliated the mercenaries. The US beat back Iranian advances and deterred attacks on the rebel group they backed.

With the US withdrawal from Syria, Russia is now the dominant military power in the most consequential conflict in the Middle East and will have a freer hand to do as it pleases. This will likely include reinforcing Iran's influence and keeping Assad, who stands accused of numerous war crimes, away from international courts.

Did the US defeat ISIS?

Senior Enlisted Advisor to the Chairman via Facebook

The US-backed Syrian Democratic Forces recently wiped out ISIS in one of its very last Syrian command centers, but the terror group remains present on the ground.

Read more: US Special Operations Command chief claims '60,000 to 70,000' ISIS fighters have been killed

That said, the territory of ISIS has collapsed to about 1% of where it stood in 2014, at the start of the US-led campaign to defeat ISIS.

The terror group remains active online and in illicit markets, but it has not coordinated large-scale terror attacks in foreign countries as it did regularly from 2014 to 2016.