<< HOW COULD the 100 soliders win against the 4,000 zulus when the 1,200 british before them couldnt??? >>
The British forces at Rourke's drift were in a superior defensive position and the engagement on the whole was far better organized than Isandhlwana (the massacre you mentioned). OTOH, at Isandhlwana the Brits committed just about every possible gaffe you could make. Moving alone in enemy territory, and with no knowledge of the location of the Zulu army, they divided their forces in half and sent one group out on a wild goose chase. The remaining forces in camp underestimated size and strength of the Zulu military and foolishly did not form a laager (i.e. circle the wagons and dig in), leaving their camp sprawled all over the face of a prominent hill. They did not employ rear guards (or even lookouts, I believe), leaving a perfect route for about 5,000 of the Zulus to sweep around the hill completely out of view from the main camp and take the British from behind, which also largely cut off their escape route to complete the slaughter.
The biggest Brit mistake, though, was their troop deployment as a whole. Rather than concentrate their firepower into a closeknit array--such as the British square that propelled them to victory later in the war--they foolishly arranged their forces in a *very* sparse formation. There were often gaps of hundreds of meters between companies, and even within those units men could find themselves spread out at intervals of several meters. In such a position, their guns were could do little to stop the charge of 20,000 fanatical Zulus. Furthermore, the defense was not coordinated; the right flank had no idea what was happening on the left and even in places were the lines held (such as the right) individual commanders often found their men isolated by the retreat of a neighboring company and were forced to pull back in turn.
Serious logistical problems compounded the situation. Ammo trains were left far to the rear of the camp so resupply was excrutiatingly slow--even when British troops managed to check the Zulu advance they were often compelled to withdraw for lack of bullets. To make matters worse, the ammo crates required a specific tool to open and these were often nowhere to be found...troops had to resort to frantically smashing at the boxes with their rifle butts to break them open. Worst of all, Individual quartermasters often refused to supply units not under their official jurisdiction so men were sent back to the front empty-handed, unable to find their own quartermaster in the chaos of the battle. It was a total disaster.
