lack of natural barriers, the Ukraine, Belarus lands are flat which means very little places to hide for the insurgency.

in Afghanistan the Taliban could hide out in network of caves and there is just no flatten mountains, the Vietcongs could utilize underground networks and dense forests to operate.

One hope for Ukraine is urban warfare, Putin launched two miserable wars against Chechnya and they were decimated from insurgents hiding out in various apartment buildings, it is likely what is stalling the advance in Kyiv.