The Anglo-Zulu War was fought in 1879 between the British Empire and the Zulu Empire. From complex beginnings, the war is notable for several particularly bloody battles, as well as for being a landmark in the timeline of colonialism in the region. This was a decisive six-month war in eastern South Africa, which resulted in a British victory over the Zulus. Before the war the Tugela River formed the boundary between Zululand and the British colony of Natal. Cetshwayo became king of the Zulus in the early 1870s. Unwilling to submit to British hegemony, he assembled a well-disciplined army of 40,000 to 60,000 men. Late in 1878 he received an ultimatum from Natal to disband his army and pay reparations for alleged insults. When he did not respond, British troops invaded under the leadership of Lord Chelmsford. Although the January 1879 rains impeded travel and the tall grasses of Zululand blocked their view, the invaders advanced into Zululand without taking normal precautions (such as scouts and sentries). The Zulu army attacked and annihilated the central British column at Isandhlwana, killing 800 British soldiers and taking nearly 1,000 rifles, with ammunition.