Fighting is underway between Israeli troops and Hezbollah fighters along the Israel-Lebanon border.

What is yet unclear: How many will fight, how long they will stay there, how many people will be killed and whether the blazing conflict between Hezbollah and Israel, after a year of bloodshed, will cross the tipping point into an all-out war. Also unclear is what it will take to secure Israel’s north enough that civilians who have been evacuated from the region for nearly a year can safely return.

What is clear is that Israel seems intent on striking a decisive blow against a terror group that has, for decades, posed a formidable threat — even in the face of potentially steep costs. Over the past year, Hezbollah has rained missiles on Israel on a near-daily basis, with Israel returning fire.