Slitherine

Correct if I'm wrong, but you can't move army 1 from province X to province Y, join Army 2 there and move on with the combined army to attack province Z.
Now you have to sacrifice two turns in the first to combine the armies and in the second round to attack. In one turn you can now attack with only two separate armies and it will not always be possible to simultaneously attack.

For that we need a flexible waiting order. So you can wait till the reinforcements have merged and after that start advancing into enemy territory.

I do not know if I understood correctly, but I did not mean that in one turn army 1 moved to another province from the army to merged with it and only in the 2nd round to attack.
I would like it to be possible to do it in one turn, i.e. you move the army, you mark its route so that it joins the other army and continues to join together in one army. Now you can only automatically determine that the armies will merge when it arrives at its destination.