^So none of the Communards, Republicans, Orleanists, Legitimists, or just generic wouldbe coupsters had the potential to ignite a civil war? I'm a little surprised at this perspective, given the reputation of French politics in this period. Or is it that the opposition to the Bonapartists would be satisfied or too fractious and divided to be a serious threat?
To ignite a civil war, you need to have big enough groups who have a kind a vital conflict with one another. When I say big enough, it means that it needs people ready to take up weapons and to form some kind of an army or a strong militia, to be able to control a significant part of the territory and its ressources, in order to fight the other.
There was no such cause and no such people in France in 1870.
The orleanists ? They were mainly moderate notables. They wanted some kind of moderate parliamentary monarchy, but a rather oligarchical one. They were the incarnation of oligarchical government. No significant part of the population would have followed them in a coup against a government established on the triumph of universal suffrage. Who would fight to have in order to have an Orleans prince on the throne of an oligarchical and business-friendly monarchy (Napoleon was business-friendly too) ?
Same for the legitimists.
The communards ? But they were mainly a parisian phenomenon, and they went to such extremities only because of the war and the terrible siege Paris went through. And in 1871, monarchists and moderate republicains (the vast majority of republicans) made an alliance in order to crush these communards because they hated these "reds" and because they represented the provinces which wanted to put an end, once and for all, to the city of Paris' claim to decide for the whole wountry.
For the republicans, it's quite different. They had good results in the elections and had some electoral strongholds, especially in big cities. But they were only a minority, and the imperial regime was popular.
To have a possible civil war, you need to ignite it not in 1870 but in 1851, when president Bonaparte made his coup. At that time, there were real fights, with touhsands of dead. Several military units refused to obey the leaders of the coup and tried to resist. A that time, if you have a few events turn badly for Bonaparte, then you can have a civil war. But it will remain very difficult because in 1848, Louis-Napoleon Bonaparte was elected president with 74% of the national vote (universal suffrage for the first time) in the first round. He was very very popular, not because of his qualities but because of his name : it was the only name known nationally and it was even the most famous name in the whole western world.