Julian II (the Apostate) and his policies

[S SEVERUS]

But Nick, that's exactly what Julian was doing! Constantius had already massed troops on the Persian frontier - he was there while Julian was raised to Augustus, for the very reason that Constantius was demanding more and more of Julian's units for that very invasion!

Had Julian remained Caesar in Gaul, and had his troops quietly gone East, then Constantius would in all likelyhood have carried out that very same battle plan - it's very unlikely that Julian, with most troops already in place for the invasion, would have turned around the existing plans.

Another reason for Julian to go ahead seems to be that the Eastern troops, only months ago going for Julian himself, were not automatically won over for him. Had he remained placid, they were likely to have supported an Eastern candidate! By going ahead with the planned invasion, he supported the eastern troops, bound them to him in a single venture, promised them the loot from Persia and had a change to keep an eye on them at one go.
IF the invasion had ended in a better result (and chances were it could have), Julian could have been a much more respected and popular emperor from at least the army's point of view.

Vortigern

I agree.