I understand the concept of a state was not fully developed during this period, but how did Rome hold itself together?
From my naive point of view it seems that wealthy individuals were often able to raise armies and initiate civil war. Were Roman soldiers just more loyal to the men who paid them? Also was there any wide spread effort to ensure loyalty to Rome through propaganda?
I've written on this subject before. The model of "client armies" in the late Republic is, at best, a contentious one, and I feel pretty justified in saying that the majority of scholars would not accept it, at least not uncritically. The seminal piece on the subject is Morstein-Marx's 2011 "Consular appeals to the army in 88 and 87: the locus of legitimacy in late-republican Rome," in which Morstein-Marx demonstrates that the troops who fought for Sulla and then Cinna, probably the best cases for the client army model, were decidedly not client armies--the army at Nola that Cinna brought to his side wasn't even under his command! I don't think there's been any dissent with this argument since. Keaveney has an earlier 2007 book, The Army in the Roman Revolution, that hangs on to certain elements of the old model (e.g. while he rejects the client army model he does accept it for armies recruited during periods of civil war), but the paradigm has definitely shifted.