So, I'm working on a dystopian TL with a POD where, instead of continuing to try to find ways to make trench warfare obsolete, various governments and scientists eventually decide that trench warfare is an inescapable fact of modern war, and begin investing in technology to make trenches even more effective, perpetuating the trenches up until present day or beyond.
Bayonets are also perpetuated by this, as is the use of poison gas.
With this, war increasingly becomes even more of a bloody, protracted, nightmarish hellscape. Politics also become increasingly volatile and countries slowly succumb to increasing instability. Developing countries who want to be great western powers study this alternate version of modern warfare, spreading the brutal gridlock of death and destruction.
However, this timeline has one problem: I don't know what technologies to advance and only have a vague idea of which ones to stagnate (tanks, nukes, missiles, and possibly certain types of aircraft) in order to realize this hellish nightmare world. I have no idea what alternate, trench-perpetuating inventions should be made, so I need a little help here...
You guys got any ideas?