Turkish Prime Minister Recep Tayyip Erdogan

Turkish Prime Minister Recep Tayyip Erdogan

Vladimir Astapkovich/Host Photo Agency via Getty Images

Relations between Turkish Prime Minister Recep Tayyip Erdogan and Syrian President Bashar al-Assad, leaders who once vacationed together, have worsened since the Syrian crisis broke out in 2011, with both leaders accusing each other of stoking instability.