Many feel it is not possible, but the games we have actually made show it is!
The base rules in the WAW engine/system allow to recreate military operations at the general and common level: movement management, stacking, combats, income, supply, production, etc… Those rules works all the time and do not need to be learnt over and over. So the learning curve is rather flat and fast. For modern wars, air rules and armor warfare are also generic, although obviously made OFF in games scenarios before the modern era.
Then each scenario has a set of limited specific rules that will fit with the time period or environment played. All the games events in a scenario are unique and assigned to each of the player, and leaders and combat or support units are also unique for each side (or the nations making one side).
Example 1: you can attack only with stacks with leaders (except for sieges and naval/air war), so managing leaders are crucial, and they are not so many. Their combat values affect battle dices, their morale values affect the battle outcome (by influencing the number of sustainable hits).
Example 2 (continued): combat works by having each unit in a stack roll a ‘dice’ and score equal (panic inflicted) or less (hit inflicted) than their combat value. This roll is modified by leader’s combat difference (if any), terrain modifiers, supports (air, artillery) and some event cards played during the battle…panicked unit no longer fight in a second round but will suffer pursuit losses. Hit unit lose one step. Number of hits (influenced by army/leader morale values and possibly cards play) determine who wins or loses.
A Scenario example! In our game Normandy 1944, movement, supply, combat and production all use the generic WAW rules, and then we have extra rules for German bunkers, Mulberries, railroad sabotage, the Bocage, naval support. And the air rules (generic) are also active.
Unique events are treated using some of the generic rules and some specific ones, and we have scripted events likes Operation Perch, German panzer ace Wittmann, DUKW, straffing of Rommel’s vehicle, French resistance, etc…
Among the units, the US 29th or 8th Infantry divisions, the 709th German ID or the 2nd SS Panzerdivision, the 4th Canadian armored, B-26 bombers, Luftwaffe land units, paratroops… all using a system of standard attack/defense value, morale value, movement value, and special combat types…all of which are generic rules in the system..
Leaders like the Americans Gerow or Cook, Dempsey or Ritchie for the British, or the Germans like Dollmannn or Rommel, and many others… here again using the combat value, morale value etc…as per the system generic rules.
Yes, ONE rule covers 90% of all instances, and in such a way the same system will be extremely familiar to players…and then each scenario/game will be unique because the look, the feel, the content, the custom and special rules and cards will lend it a special and original flavour!