Since the outbreak of the Syrian civil war in 2011, Iran and Russia have become the Syrian government's principal allies in the conflict, openly providing armed support. Meanwhile, Russia's own relations with the West plummeted due to the Ukraine crisis, the 2018 Skripal poisoning incident in Great Britain, and alleged Russian interference with Western politics, prompting the U.S. and Europe to retaliate with sanctions against Russia. As a result, Russia has shown a degree willingness to ally with Iran militarily. Following the JCPOA agreement, President Vladimir Putin lifted the ban in 2015 and the deal for the S-300 missile defense system to Iran was revived. The delivery was completed in November 2016 and was to be followed by a $10 billion deal that included helicopters, planes and artillery systems.