pre-emptive strike. That what it would be called to day. But don't forget the British were building an empire.
And those famous words.
"Lord Chelmsford invaded Zululand without the knowledge of the British Government in the hope that he could Capture Cetshwayo, the Zulu King, before London discovered that hostilities had begun"
So it was not the British Government's intention to go to war in 1879. But that had no choice but to continue and back the invasion.