The Grand Army of the Republic was succeeded by the military of the Galactic Empire and subsequently the First Order. Assuming these three military forces to be different incarnations of the same entity, how has this entity's warfighting capabilities changed over time?
By warfighting, I'm therefore looking at said entity's effectiveness at waging wars and winning battles. They are soldiers, not peacekeepers. Possible aspects to consider can include training, technology, qualities of the individual soldier, skill with strategy and tactics, quality of the generals and officer corps, and other aspects which I may not have considered.
In other words: How well would each incarnation fare had full-scale galactic war (Clone Wars scale) broken out within their own respective time periods?