It was WW1 which opened the cracks in the system of empires that dominated the world. If Europe somehow missed this cataclysm, the old imperial systems would survive much longer. Germany and Austria-Hungary would probably liberalize somewhat, while Russia might not.
However, the growing contradictions between heriditary monarchs, evolving parliaments, and the cost of maintaing overseas empires would place severe strains on the imperial systems. While wars involving direct conflict among the European powers in western and central europe might be avoided, I would suspect conflicts would continue along the margins of the empires. This, together with the continued rise of independence movements and the relative liberalism of the British, French, and American colonial empires would lead to these main western powers being increasingly bogged down in conflicts against national liberation movements wanting full independence rather than liberalized colonial rule. They might gradually abandon their imperial pretentions when the cost in money and manpower to maintain them became political issues back home. Quite likely this would lead to wars between the Japanese Empire and one or several Euro-American powers as Japan attempts to fill the vacuum. London. Paris, and Washington might well come to terms with independent - but allied and puppet - former colonies. Having them come under the control of Japan would be another thing entirely. The Ottoman Empire would still probably be reduced, but more gradually. It would not be unthinkable that a reduced Ottoman Empire - one which still held the oilfields of Mesopotamia either directly or thru local spin-off states - might still be an important player - especially of some sort of "Kemalist" reform still occured. Assuming Imperial Russia could survive the "Red" revolutions - which I think is very likely in a world without WW1 - it might be the dominant world empire by the mid-20th century - I tend to think a vast continental empire would be cheaper easier to maintain than a vast maritime empire such as Britain's. Without WW1 (and WW2) the USA would probably remain largely detatched from international relations, perfectly happy to lord over client states in Latin America and not be bothered at all with Europe. I would only see the Americans directly allied with a European power if the enemy was Japan in the Pacific.
There would probably never be a UN or organization like it. Rather, there might evolve a system of annual summits among the major powers (Russia, UK, France, Austro-Hungary, Italy, Germany, Japan, the USA, and perhaps one or two others) where border disputes could be mediated, military balances agreed to, and trade relationships etc. discussed. Sort of an intermittant Security Council without the rest of the UN to mess things up.
The USA and Russia might still become the "superpowers" in this world, both because of their large continental populations and the abundant resources in the contiguous areas they dominate. Presuming nuclear weapons do not exist (which I think is at least possible), the world power structure would not become nearly as bi-polar as in OTL, but the USA and Russia would have tremendous influence.
Terrorism would be the only means for the have-nots to get the attention of the empires. It would increase, and assuming technology in travel and communications developed roughly along the same lines as in OTL (allowing perhaps for somewhat slower development of some military technologies), national liberation movements would be able to strike anywhere, not just in their own homelands.