The Zulu did have weapons, particularly after their victory at Isandhlwana; they simply didn't have enough of them, nor ammunition sufficient to supply every soldier.

According to contemporary accounts, Cetewayo's army was composed of 40,000 men. It's some measure of British arrogance that when Lord Chelmsford started to march into Zululand in January 1879, he did so with only 5,000 European soldiers and 8,000 armed Africans ─ then divided that force into three columns.

The battle at Isandhlwana annihilated one of the columns, but the column at Ginginhlovu fought its attackers to a draw. At Kambula, the third column won a decisive victory over its opponent.

The British briefly retreated, then returned six months later with 10,000 new European reinforcements plus additional African levies, and the issue was not in doubt.

George Washington University's David Silverman has studied the spread of firearms across North America in what he calls the "gun frontier," and if you listen to him talk, he explains that the spread of firearms is driven by trade and the inability of early modern nations to stop that trade. By the late 1800s, nations were better able to halt or slow the firearms trade.