Since the Syrian Civil War began in 2011, the United States has played an active role in the conflict. The US has provided both military and diplomatic support to the Syrian opposition and has taken an increasingly more direct involvement in the war.

The US has provided both financial and military aid to the Syrian opposition since 2012. This has included both lethal and non-lethal aid. The US has supplied weapons, training, and other military equipment to the Syrian opposition, as well as providing financial support to the opposition forces. The US has also provided humanitarian aid to civilians affected by the war.

The US has also provided diplomatic support to the Syrian opposition. The US was an early supporter of the Syrian opposition, calling for President Bashar al-Assad to step down and for political reforms to the Syrian government. The US has also taken the lead in negotiating a cease-fire between the Syrian government and opposition forces.

In 2013, the US began a military campaign against the Islamic State of Iraq and Syria (ISIS). The US has provided air support, weapons, and training to the anti-ISIS coalition, which includes the Syrian opposition. The US has also provided airstrikes in Syria and Iraq against ISIS.

In 2015, the US began a direct ground intervention in Syria. The US has deployed special forces units to assist in the fight against ISIS and has provided logistical and intelligence support to the Syrian Democratic Forces (SDF). The US has also provided air support and weapons to the SDF, as well as providing training and equipment.

The US has also played a role in diplomatic efforts to end the conflict. In 2012, the US and Russia brokered a ceasefire between the Syrian government and the opposition. This ceasefire was followed by the Geneva II Peace Talks in 2013 and the UN-sponsored Geneva III talks in 2014-15. The US also supported UN Security Council Resolution 2118, which established a framework for dismantling Syria's chemical weapons stockpile. 

The US has also provided diplomatic support to the Syrian opposition in the Geneva peace talks. The US has pushed for a political solution to the Syrian conflict, which would include the transition of power from Assad to a more representative government and the establishment of a new constitution. The US has also provided support to the UN's humanitarian efforts in Syria and has been a leader in the effort to hold Assad and his allies accountable for war crimes.

Overall, the US has played an active role in the Syrian conflict, providing both military and diplomatic support to the Syrian opposition and taking direct involvement in the war. The US has also been a leader in the effort to bring about a political solution to the conflict, and in the effort to hold Assad and his allies accountable for war crimes.