Simply put, CA make enough money for SEGA.
That means that we'll see more TW games until SEGA don't see it as worthwhile in supporting them - e.g. poor sales.
I think TW games are most suited to the ancient period to about 1900, as the main arms for fighting are infantry, cavalry and (mostly) direct fire artillery of various forms, which are easier to model.
WW1 would be too complex to fit into the TW model, the battles would be fought on the strat map, because how can you model a battle like the Somme that started in June and ended in November? Small engagements wouldn't cut it for me because the bigger picture is much more important in this time period.
That still leaves us with a lot of time left to play with. I can see there being a lot of downloadable content for the current period, inc napoleonic, US civil war, opium wars etc.
TW hasn't looked at China & surrounds yet, and will probably revisit the Ancient World again next as this is probably the next popular period of history.
Got to say as well that I am one of the lucky ones and have only had 1 CTD when a savegame wouldn't work, and got round it by using the last autosave.
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