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human
[Star Wars] Why wasn't the Rebel Alliance larger?

Why is it that the rebels are so hopelessly outmanned by the Empire? 

The rebels always seem to base themselves off the grid on far away planets like Dantooine, Yavin 4 and Hoth despite the fact there are larger more populated systems they can base themselves such as Bespin or Alderaan which would prove a lot harder to launch an attack on, hell they could even have set up base in Hutt Space and get them involved.

The rebels seem to be based only at one place at all times, why are there not more rebel factions throughout the galaxy?

The empire is extremely humanocentric. Why would any alien creatures let humans rule over them and treat them like scum? Why are the Ithorians, Zabraks, Wookies, Bith, Hutts, Rodians, Trandoshans, Twleks etc not creating their own freedom forces or joining the alliance? Surely the planets with an alien majority wouldn't want empire rule? Surely most planets in the galaxy are an alien majority??

Surely there must be planets out there with sizeable armies and technology that can protect themselves from a few Star destroyers? Why haven't they joined the rebels? 

I don't agree that the Galaxy is frozen in fear of a Death Star destroyed by a small fleet of X-Wings or a cyborg old man who worships ancient religions and magic powers? 

If a few pilots, a wookie, a smuggler, a princess and farmer from Tatooine can take down the empire I think a huge combined army of aliens threatened with genocide would have finished the war a tiny bit sooner.

Why was the alliance so small!!??
gpt
The Death Star wasn't the only thing that Rebels were afraid of. The Empire had a variety of tactics, such as Base Delta Zero, where they used Star Destroyer turbo-lasers to glass a planet from orbit. They also used biological weapons to devastate dissident planets. 

Many planetary leaders and high level politicians were active supporters of The Empire, as it boosted their own power or lined their wallets. 

The Rebel Alliance was a loose conglomeration of smaller, localized rebel groups. Until near the end of the war, they lacked funding, resources and an organized power structure. 

Let's say for example that Alderaan decided to openly defy The Empire. Most likely the Imperials would use their intelligence service to remove the ruling house from power via threats and bribery, then install puppet rulers in their place. That's if the local Moff didn't just decided to glass the major inhabited areas and let them be an example about why you shouldn't turn against The Empire. 

The Hutts would have had no reason to get involved. The Empire brought back slavery, and slavery is good business. Smuggling also became a larger trade, due to restrictions put in place be the imperials. The Empire unintentionally generated a lot of revenue for the Hutt Cartels.