In front-line villages of south Lebanon, the posters of Hezbollah members killed fighting Israel 10 years ago still stand, but have faded. Now rising up around them is a new generation of posters, bearing the faces of young fighters from the militant group killed in Syria.

They reflect the Shiite group’s radical shift from decades fighting Israel, a cause that at one time earned it soaring popularity across the Arab and Muslim world, to the far less popular role fighting fellow Arabs in defense of Syria’s president, Bashar Assad.

It is a venture that is proving costly. The war in neighboring Syria is bleeding Hezbollah of fighters and experienced military commanders, and has left the group more vulnerable to accusations of complete subservience to Iran, which rallied Hezbollah to intervene in the war. So far, more than a thousand of the group’s fighters, including several founding members, have been killed in Syria, a toll higher than the one incurred by the group in nearly two decades of fighting Israeli occupation forces. […]