I agree with Gargantua that a dice-roll simulator designed for a WWII board game doesn’t sound like a realistic mechanism to handle the military aspects of a modern international-relations simulator.
It’s hard to offer advice on what your best option would be without more information on what you mean by “the military portion of the simulation”. What types of military actions are you planning to model? Peacekeeping / peace-making operations? Small local battles? Full-scale wars between just two countries? A general conventional war between multi-country alliances (along the lines of NATO vs. the Warsaw Pact)? An all-out nuclear war? These different scenarios would require vastly different simulation methods.
Keep in mind that, as a general rule of thumb, games / simulations which put the players in high-level roles (like the political and military command authorities of entire countries) tend to have highly abstracted battle systems in which engagements are fought between entire armies or army groups and in which combat is sometimes resolved simply by comparing the gross ratios of the forces involved. If that’s the level at which your simulation will operate, you may not want to bother with a detailed model that takes into account the tactical-level niceties of what unit fired at what other unit.