I usually like alt-history, but WW1 is much too big to answer. Usually, you can at least somewhat ignore some factors.
But WW1 killed 40 million people. Even if you only look at the "important" persons. just look at the expressionistic intelligentsia killed (many yearned for a "cleansing" war that burned down the old order and died in the first few months) or at the lost generations of the best and brightest in Germany, France, the UK or Russia? How many Atatürks, Brusilovs and Remarques died in that senseless slaughter?
I am normally of the opinion that small changes even out and single people rarely change history against macroscopic trends. But can you really do that with 40 million deaths on the, at the time, most advanced continent on Earth? Even if we disregard political developments, how could you ever discount the people getting slaughtered in this war?
Hitler almost died in WW1. He's probably the single most chosen guy to eliminate via time travel. How many like him did die in WW1? How many of his assassins did? How many events were prevented that could have stopped his rise to power?
We can look at events that happened because of WW1 (no German colonial empire, rise of Japan, rise of the US, WW2, German nazis, Russian communists, Italian fascists, European brain drain, decolonisation etc.), but that doesn't make the reverse true. No WW1 doesn't make Austria-Hungary a stable country or doom Africa to be an eternal colony. But does it make the change slow enough to allow the rulers to adapt? Would France lose Algeria without the wars? Would the UK lose India? Probably. But how?
So what happens if WW1 doesn't happen? Everything.
Any answer beyond that is entertaining fiction, but nothing else.