For Europe you could use easy trick - 4 centers (Germany, France, Italy, UK) divided by large mountains or large water. Only exception is west Germany land bord

For Europe you could use easy trick - 4 centers (Germany, France, Italy, UK) divided by large mountains or large water. Only exception is west Germany land border. It become early obvious, battle on mountains or coast battle are ineffective. So, most European battles happen on flat land.