I don't recall the Thalmor attacking Morrowind heavily. Valenwood, Black Marsh and Eleswyr left on their own after Thalmor-backed coups tore them from the empire (...Just like in Skyrim if the Stormcloaks win. Read that Ulfric dossier.). And the Empire did help Hammerfell. Do you really think they could have resisted the Thalmor without all those "discharged" legionnaires?

4E 29 — The Aldmeri Dominion is recreated after Alinor and Valenwood proclaim a union, and all contact is severed with the Empire.
The union came about after a Thalmor-backed coup overthrew Valenwood's government. The Empire and its Bosmer allies are caught off-guard and defeated by Altmer forces that invaded Valenwood following the coup.

4E 98 — The two moons of Nirn, Masser and Secunda, vanish for two years in what becomes known as the Void Nights.
4E 100 — The Void Nights end, with the Thalmor taking credit for the return of Nirn's moons.

• The Khajiit credit the Thalmor as their saviors and Imperial influence in Elsweyr begins to wane dramatically.

4E 115 — The Elsweyr Confederacy becomes the two kingdoms of Anequina and Pelletine, which the Aldmeri Dominion accepts as client states.

I don't recall the Thalmor attacking Morrowind heavily. Valenwood, Black Marsh and Eleswyr left on their own after Thalmor-backed coups tore them from the empire (...Just like in Skyrim if the Stormcloaks win. Read that Ulfric dossier.). And the Empire did help Hammerfell. Do you really think they could have resisted the Thalmor without all those "discharged" legionnaires?

No, but they had the Argonians to do that for them, after Black Marsh had come under Dominion control. Still the empire stood aside and did nothing.

Both sides ignore the Thalmor and at least the Stormcloaks talk about preparing to fight against them at the end, can't recall what the Imperials said on the Matter.

Sorry but where is it stated that the Thalmor control Black Marsh? If I recall, Black Marsh is independent from the Empire and Thalmor