Belarus joins the war and invades Ukraine. eventually Ukraine beats back Russia after a few more months of fighting and decides to invade Belarus so Russians do not have a safe haven to their north, so Ukraine does not have as much border to defend, and so kyiv isn’t as accessible to Russia. also they invade to get back at putin by overthrowing his puppet regime in Belarus so putin has to deal with another potentially west friendly nation on his doorstep near Moscow.
The military in Belarus is fairly small and I wonder if they’d support the government of lukashenko in an invasion.
Ukraine has their hands full just defending right now and I don’t foresee an expansion into offensive siege and occupation tactics soon. They lose the home advantage. It would certainly also embolden the Russians: “See!? They did invade their neighbor, too! Begin the indiscriminate shelling!”
I’d be more interested in whether Ukraine could launch attacks into Russia itself, if only to make the war more costly to Russia. Probably a bad idea but it would depend on the circumstances.
The thought occurs that if Russia pulls most of its troops out of Belarus towards Ukraine’s eastern flank that might be a good opportunity for the Belarusian army to oust Lukashenko. I would really like to see them cut the puppet’s strings.