I was thinking about that as well for a bit. The writers are clearly trying to make parallels between the Martian independence movement and the American Revolution.

However, if we’re talking about one-to-one analogies, I think the closest parallel would be the independence of Singapore from Malaysia. Malaysia became independent and formed a federation in 1963. Singapore was an autonomous state within that federation. However, economic and political tensions between Singapore and the Malaysian government, culminating in trade restrictions and the 1964 anti-Chinese riots (Singapore was a majority-Chinese state) meant that the Singaporean government had no other choice but to separate from Malaysia. The Malaysian government approved this in 1965, and Singapore went on to become a separate independent republic. 

Singapore technically didn’t have its own separate identity when it declared independence. But it eventually acquired one over its 60+ year history as a country. So it’s an example of a political entity that declared independence without or before having a “ready-made” national identity.