The events from Ent S4 are equivalent to the french declaring war towards the germans in 1937.
The French declared war on Germany in 1939, while Germany at that timepoint wanted nothing but peace with them. This by no means suggests that the French were aggressors with conquest plans, or that the Germans were victims without plans for conquest.
Earth fought a defense war against the romulan agression. In the end, it may have retained 'buffer' territories as defense against a continually aggressive empire.
That sounds heroic and epic and sympathetic and whatnot - and at the same time utterly unconvincing. Hard proof for this is completely lacking. And so is the "heavy implication" in the source material, unless one's viewpoint is bigoted from the start.
Just because Earth feared invasion during the war doesn't prove they didn't start it. It may just as well be that they came close to reaping what they sowed.
Then each victorious country in history - no matter its reasons for entering the was - fought a conquest war.
The definition would be narrower than that. If the victor didn't gain new territories at the conclusion, then the war wouldn't have been a successful conquest campaign. If the victor never gained any territory, then the war wasn't even an unsuccessful conquest campaign.
And none of this relates to the question of who started the war, and to what end. All options are currently open: Romulans starting a conquest campaign, or starting a defensive war, or responding offensively to an Earth aggression that did not involve any territorial ambitions, or responding defensively to an Earth conquest campaign, etc. etc.
And the federation/starfleet did not just kept the secret about the romulan appearance - it didn't know how the romulans looked like.
Perhaps, perhaps not. Since the very concept of the Romulan faces remaining hidden is so difficult to buy, virtually any conspiracy on the vein that the knowledge was suppressed sounds preferable in relation.
Timo Saloniemi