Military destruction is rarely an arbitrary twist of fate; rather, it is often the devastating result of a nation's own political and spiritual choices. A striking sword is simply the harvest of distancing oneself from God and making deeply flawed decisions.
The primary approach among commentators is that a sword of judgment will fall, rest, and firmly establish itself within the cities of Israel [רש״י, מצודות, אבן עזרא, רד״ק]. It will not merely pass through, but will be found dwelling among the people [ביאור שטיינזלץ], bringing about total consumption and complete annihilation [מצודת ציון].
This destruction is compared to the violent cutting down of tree branches [אבן עזרא, מצודת ציון, מלבי״ם, רד״ק, שטיינזלץ]. Commentators offer different views on what these branches represent in the life of the nation. One approach views the imagery geographically and demographically: if the central city is the trunk of the tree, the branches are the smaller, dependent villages surrounding it, or the residents and children of the city itself [רד״ק, מלבי״ם, שטיינזלץ]. Another perspective interprets the branches as a military metaphor, representing the mighty warriors of the nation who will be completely wiped out in battle [רש״י, מצודות].
The root of this disaster lies entirely in the nation's own plans. The traditional chanting notes of the text place a unique double emphasis on this concept, framing the cause of the tragedy as a profound, standalone declaration [רש״י]. The sword consumes the people solely because of the bad advice and flawed strategies they themselves devised [אבן עזרא, שטיינזלץ].
Commentators differ on the exact nature of these destructive plans. It can be understood as a spiritual betrayal, where the people abandoned the worship of God in favor of idolatry [רד״ק]. Others point to a massive political and strategic blunder. Instead of relying on God, the nation's leaders sought out military alliances and begged for help from the kings of Egypt. It was this exact diplomatic maneuver that provoked the King of Assyria to attack and exile them. Ultimately, the people brought the ruin upon themselves by their own hands, leaving no room to cast blame upon God [מצודת דוד, מלבי״ם].