It’s very difficult to assign stock market moves to any single event - we all love to do it, but ultimately it’s impossible to isolate say an invasion from high inflation, from that days company results etc.
But in general I’d say my base case would be for a relatively small fall in developed market stocks - maybe more in Europe, then UK and US with smallest impact.
However if you believe any invasion would be limited in scope, and not invoke WWIII then it could be the markets could ignore the event or even rise - given it removes some uncertainty.
Yes, if you put aside the sheer horror of any fighting and bloodshed and view this simply as a (dangerous) political game, market falls and lower share prices than a month ago might be seen as an opportunity for investors.
Or…is the Ukraine crisis just a distraction from the bigger economic/financial picture for markets?