WWI hastened the fall, but remember that by 1910
1. The USA was already on track to replace Britain as #2 economy
2. Germany had replaced Britain as #1 economy
3. The Brits had set themselves up as a “moral force” and that they were “civilizing the world” — so they were in a twist when British forces committed massacres such as in the Boer war (first concentration camps) or the Jallianwalla Bagh massacre (when Gen Dwyer fired on civilians)
IF WWI had not happened, the UK would still be where it was in the 1960s — the colonies were going to go away.
“What if” is always a tough sled....
World War I rewrote the map of Europe (and really the world) in so many ways—hard to figure out what might have happened if there was no war.