The division of the unified monarchy into the Kingdom of Judah and the Kingdom of Israel sparked a deep and lasting rift characterized by constant military tension. Throughout the lives of Rehoboam and Jeroboam, a state of continuous conflict existed between their two nations.
This ongoing hostility presents a historical challenge. Early in the division, the prophet Shemaiah strictly forbade Rehoboam from launching a military campaign against the northern tribes. The people obeyed this prophetic command, recognizing that the splitting of the kingdom was a direct decree from God. If they listened to the prophet and stood down, the presence of a constant war seems contradictory.
The primary approach among commentators resolves this by focusing on the timeline of events. The prophetic restriction was only meant for the immediate aftermath of the split, when Rehoboam had not yet accepted the reality of the divided nation and wanted to force the entire kingdom back under his rule. While he initially obeyed the prophet and held back his forces, this peaceful stance was temporary. As time went on, he eventually took up arms again, leading to ongoing wars that lasted until the day he died [רד״ק, מצודת דוד, אברבנאל].
Another perspective suggests that the ongoing conflict was not a formal, organized military campaign. According to this view, the prophet successfully prevented Rehoboam from deploying a regular army to crush the northern tribes before they could fully organize. However, the deep tension remained unresolved. The continuous fighting actually consisted of frequent violent clashes and mutual border raids that took place regularly along the shared boundary between the two kingdoms [ביאור שטיינזלץ].