What happened in 2011 to aid growth of ISIS?

In 2011, the outbreak of the Syrian Civil War created a power vacuum and chaotic conditions that facilitated the rise of ISIS. The group exploited the instability and sectarian tensions, gaining territory and recruits by positioning itself as a Sunni extremist alternative to the Assad regime and other opposition forces. Additionally, the withdrawal of U.S. troops from Iraq in late 2011 allowed ISIS to regroup and expand its influence in the region.