I'd add that there is continuum of options to provide support to a party of a war: from zero support to joining the war in full force as an ally. At which point

I'd add that there is continuum of options to provide support to a party of a war: from zero support to joining the war in full force as an ally. At which point the support amounts to a proxy war is up to a debate. Also, I think that it does matter who started the war. Those who are fighting, those who provide support or neither of them (that is, the other party of the war).