You have to pick the units you want to use and left lock them on the order. Then they should be assigned. Also don’t forget to stop drilling and let your troops regain supplies and organisation (the two bars next to the unit on the left) before attacking/declaring war. Otherwise they will be pretty helpless!
I gonna try. For the moment Italian win in ethiopia even if they have a gap 1 against 4 for UK. Samething in Egypt wher 18 division can't beat 2 even if the french took 75% of the italian north africa....