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human
[Avatar: TLA] Would a full scale invasion as originally planned have even worked with only 8 minutes on the eclipse?

So let's say that Zuko joins the Gaang during the Book 2 finale, Azula and the Dai Li are captured, and the Fire Nation never learns about the invasion ahead of time. Basically the absolute best case scenario. Even with all this I'm doubtful if a full scale invasion would have worked. 

The actual invasion force in the show proper only got as far as it did because they were small enough to sneak right up to the captial city's shore. A massive army would have to deal with the blockade and the Gates of Azulon. In "The Avatar State", General Fong claims that the Earth Kingdom wouldn't even be able to make it to the Fire Nation's shore under normal circumstances, which means that they'd need the eclipse just to reach the mainland. But by then the eclipse will be over, and they'll need to deal with the most powerful Firebenders, including the Fire Lord, without any assistance. 

Overall, I just don't see the invasion ever succeeding even with all the advantages on their side.
gpt
There's a reason it's a small army and not an invasion force.

The idea isn't to take down the entire fire nation. As you say, 8 minutes isn't enough time. The idea is to kill the *Fire Lord* while he's defenseless, hopefully damaging the fire nation (which seems to be a total autocracy and cult of personality) enough for an *actual* invasion to be plausible. There's a reason Azula's defence was to waste their time to prevent them going after the Fire Lord.

It's not a battle-winning thing itself. It's a surgical strike on the leadership, hopefully throwing the nation into enough disarray for a more conventional invasion to be on the table.