Tick off Historical Attrition.
Make sure you have wagons.
TYW uses the 'simple supply' system, which means if you mainly have played newer topics, they whole supply situation is different. Supply is not forwarded, it is only local. So you need to do some counting of unit elements. Place this against the supply output of regions your forces are in and adjacent too (absent other of your forces). The number of elements must be lower than the available supply.
Once you get a feel for this very different supply system, it works just fine. Find a player of WIA or AJE to get a sense of how to make this work. But when not in a balance of elements to supply, get some wagons to extend your supply.