Bring the Spanish Influenza ahead by seven years such that by 1913 there are 70 million dead around the world and global medical authorities have to work together to fight the disease. Avoid the opening of the war by having the royalty of Europe afraid to venture outside of their palaces while the global network of trade slows markedly due to fear of the disease. Afterwards the recovery leads to a global recession, causing an earlier focus in synthetic chemistry that causes certain goods like rubber, oil, and polyester fibers to be made in the 30s and 40s instead of the 40s and 50s. Overall it will slow technology markedly and cause the Russian Empire to keep the Czar a while longer, but you could see a world by the 1960s with technology akin to the late 1930s/early 1940s where decolonization has not happened with few exceptions. The world has not known a major international war since the Napoleanic era though storm clouds are on the horizon and anything is possible...