Was the fall of rome inevitable?

Hey im writing an essay on this. my thesis is basically that rome was getting too big for this kind of a centralized government. my first paragraph will be mainly about how the military contributed such as how it was comprised of mercenaries. and the barbarians. cant forget them. another paragraph be about the economy. i was thinking like how it was too big of a bureaucracy to pay all these people and stuff. could use help on this like examples and what not. my third body paragraph will be about politcal problems. help me out there. no idea what to do there. Thanks. just give me examples and suggestions.