The Boer War escalated into guerrilla tactics after occupation.

Evidence

The war in South Africa meanwhile continued. … Roberts and Buller had hardly left the shores of South Africa when the war flamed into swift-moving, hard-hitting guerrilla. — Winston Churchill, A History of the English-Speaking…, 1969

Categorization

• corroborated: 2 independent passages support this claim — Winston Churchill, A History of the English-Speaking…, 1969
• XREF: connects to: Guerrilla tactics in the woods devastated traditional European line infantry.; British surrender at the Boer War peace ceded native policy to Boers