Why did Alexis Tsipras resign in August 2015?

Alexis Tsipras resigned as prime minister of Greece in August 2015 primarily due to a loss of support within his own party, Syriza.1

Following the debt crisis, Tsipras negotiated a new bailout agreement with Greece's international creditors. When the final version of this agreement was presented to the Greek parliament on August 14, 2015, nearly one-third of the members of his own party either voted against the measure or abstained.12

Faced with this internal desertion, Tsipras chose to resign on August 20, 2015, shortly after the first tranche of the new bailout was received. His goal in stepping down was to trigger a snap parliamentary election, through which he hoped to secure a fresh mandate from the Greek people to continue his leadership.12