As the Islamic State massacred its way throughout Iraq and Syria this summer, a separate battle took place in neighbouring Lebanon, as IS fighters invaded the Lebanese border town of Arsal, beheading captured soldiers and unleashing waves of lethal car bombs.Hezbollah, one of the world's strongest guerrilla armies, has also become involved—the group is either defending Lebanon or making things worse, depending on who you ask.VICE News traveled to Lebanon to explore the battle being waged by one of the world's fiercest militant groups against one of the Middle East's smallest and most fragile nations.