The main problem with strategus is, and always has been that once you loose control of your fiefs it is almost impossible to get back into the fighting again (unless you have allies of course). This simply has always forced people to ally together to survive, or surrender their sovereignty to a larger faction. This is how the original Templar Bloc was built, it is how the UIF came about, and it hasn't changed since.
Once you have take control of all your opponents fiefs, its basically game over for them. They can always go begging door to door, attempting t build up an army, but that normally results in building an alliance with those who can provide them with troops. Lets be honest, who's going to give troops to someone who they can't call to their side later who they don't consider 'friends'.
A solution to this is to remove the 'recruitment' system and instead implement levies of some form. Fiefs with different prosperity, size, location etc. provide different size levies. Levying the troops from a fief for extended periods decimates the productivity but also causes discontent. Discontent means that members of the population will be available for levying in the area at 'hideouts' by neutral players who wish to be bandits or mercenaries.
This would allow for a distinction between 'conquest' (in which the population is destroyed, discontent is reduced and the prosperity ruined), 'raiding' (in which the population is unaffected, discontent increases sharply and prosperity is barely damaged) and 'capturing' (the population is reduced, discontent is increased and prosperity is damaged)
The challenge in strat now should be about holding onto your fiefs while expanding. Regions that have not been ravaged by war should also have increasing discontent as the peasants clamour to regain their independence from their lords, the longer an area is at peace the more 'rebels' become available to independent clans / neutral players.
This would allow small clans to set up near a village which has not been involved in war and gather the peasants to them in a revolt against the oppressive Lordship of the coalitions. Castles should be the least likely to rebel, being the rightful holdings of their lord, yet discontent should be present. Maybe small bands of young, relatively well equipped 'hedge knights' appearing and causing a bit of trouble around the area and maybe finding themselves a lord at the same time. Towns should also offer distinctive opportunities. The ability to hire mercenary forces at great expense who are well armed but in small numbers, enough to defend your caravans or attack the evil alliance forces I'm sure.
tl;dr : You should be able to get troops without holding a fief, or without having to be friends with someone who is in control.
