That's a bit like pissing on someone and telling them it's really just a nice warm shower . Slavery, genocides, exploitation, artificially drawn lines in the dirt and subjugation didn't benefit 3rd world peoples. Many parts of the 3rd world were advanced well before the West,and provided for crucial scientific knowledge that uplifted the West.
WWI shattered global systems of government that were the norm from the late Stone Age up until then by devastating the traditional Empire structure in an irreparable way. It took the regular people of Europe being thrown against the meat grinder of industrialized modern war to finally say "enough!" Some chose to try out socialism, some democracy, some military dictatorships, etc; but the old method of kings and queens making land grabs just wasn't viable without enormous human cost. WWII, which in my opinion was really the final stage of the Great War, cemented this idea.
As far as benefitting third world peoples, of course there were hardships. Removing entrenched power from any place is going to be messy, and some were far better at it than others. The British Empire will be remembered fondly in the future. Everywhere they went, they ended slavery, brought education, rule of law, infrastructure, commerce etc and vastly improved the lives of their subjects. Its a mixed bag, for sure; but they'll be viewed more like the Romans than the Mongols. If you read the history from the Scythian or Gaulish side, sure; it wouldn't sound as nice, but it was Roman colonization that dragged a bunch of nomadic horse archers and headhunters into what was then the modern world. If the British Empire hadn't have been the dominant power, you'd still have plenty of multiculturalism with segregated European aristocrats with one culture ruling a culturally intact horde of serfs. Instead, the Brits spread the idea that all life has value, and that no man should be a slave.
Those colonized by the French and Spanish aren't faring so well. They set up aristocratic models where certain citizens are simply worth less than others rather than those in English speaking countries, and its taking them a bit longer to get their feet back under them. In America, for instance, we are the remnants of three great colonies and smattering of smaller ones smashed together by a revolution and welded together by a Civil War. The old French and Spanish colonies were the ones overwhelmingly in favor of slavery. We are still dealing with the consequences of that today.
