What's the point of nuclear weapons in colonial conflicts? They destroy the cities the imperial power wants to occupy. If WMDs are to be used in colonial conflicts, then the imperial power would prefer chemical weapons, so they can kill rebels and the local population while leaving the infrastructure intact (or contaminated but intact, depending on the chemical agent)WW1 never happen. Tensions are simmering but never escalate or a more limited Balkan War is a horrifying example of industrial warfare.
Point is all the European nations need a new "limited valve" for tensions. This slowly leads to a consensus in international politics that allows "colonial wars" and proxy wars without triggering a wider war that would affect the European continent.
The 20s, 30s and 40s are full of fleet actions, limited colonial offensives etc. The arms race continues. Sure, sometimes it is slowed down due to the economy but tanks and the first jet prototypes etc. all were developed at similiar times compared to OTL.
The European nations (Russia too depending on what one defines as European), the USA and Japan all start nuclear weapons programms in the 40s. In India tensions are really boiling over in the late 40s. In the early 50s a massive Indian revolt happens and after some initial victories Britain realizes that the conventional military approach isn't working. Desperate the nuke is used to intimidate the revolution/rebellion and it works for a while.
This breaks the "taboo" of using nukes (that taboo never really developed ITTL) and tatical nukes and strategical nukes are liberally used in colonial conflicts.