During the 1880's, bullet design was reaching it's limits. The lead alloys then used could only be pushed so fast, as the lead would strip off and foul the bore. The need for speed was to flatten the trajectory of the bullet, which sailed in a huge arc over large distances. The need for a flatter trajectory was obvious, as fiddling with sights in a battle is not productive.
The Brits took an interest in Major Eduard Rubin's work in Switzerland, where he was working on a 7.7 mm design, which enclosed the lead in a metal jacket. This solved the velocity problem as the copper jacket held the bullet together, and with the smaller bullet led to a flatter trajectory. His straight walled case design proved less than satisfactory, so a bottle necked design was used.
The new bullet was also used in their new magazine rifle, the Lee-Metford. Magazine rifles were finally being embraced by the conservative men in power as actually being necessary, as undue ammunition expenditure was previously thought to be frivolous. Of course, they also insisted on a magazine cutoff, keeping the extra rounds in reserve. Hard to break old habits.
The new combination came up short in action, however. The bullet design still had anemic velocity to be a real man killer, plus the fact that it didn't look big enough compared to their old .450/.577 rounds. The size of the lead bullet seemed to be the answer. The old bullets with no jacket expanded some in human bodies, so that was seized on by Captain Clay, who worked in the arsenal at Dum Dum, India. The name stuck, as synonymous with expanding bullets of any kind. The jacket was removed from the bullet tip, with the possible expansion of the bullet now possible on impact. The original experiments were a failure, as the jacket didn't cover the base of the bullet, and sometimes were left in the bore.
However, the Brits did solve this problem, and made an effective expanding bullet. Then the world howled in protest, led by the Germans, and the use of expanding bullets were banned in war by the Hague Convention, in 1899. Undeterred, the Brits still wanted stopping power, and the development of nitrocellulose powder, bringing much higher velocities, and new bullet design that would let the bullet tumble on impact was the answer.
So the Hague Convention was effectively defeated. However, war is war, and there really is nothing humane about it. Unnecessary suffering is the name of the game. Men in armies since have tried to stack the odds in their favor by making homemade expanding bullets on their own. Usually filing a cross in the point of the bullet, it may not have performed better, but it made the men feel better about their chances.
Which brings us to today. Troops now stationed in Afghanistan have been caught with hollow point ammunition and are being punished, while everyone at home with a self defense pistol and even the police are using hollow point ammunition. The only humane thing to do is to stop this war nonsense, though I think that will not happen in my lifetime.