Sentence Correction

Had the United States allowed the California Republic to remain independent after the Bear Flag Revolt rather than annexing it with military force, this "California nation" might have become the wealthiest nation in North America.

A Had the United States allowed the California Republic to remain independent after the Bear Flag Revolt rather than annexing it with military force, this "California nation" might have become

B With the United States annexing the California Republic after the Bear Flag Revolt instead of allowing it to remain independent, this "California nation" didn't become

C The United States annexed the California Republic after the Bear Flag Revolt and didn't allow it to remain independent, to prevent it to become

D The United States didn't allow the California Republic to remain independent after the Bear Flag Revolt, it annexed it with military force instead, and this "California nation" didn't become

E The United States, by not allowing the California Republic to remain independent after the Bear Flag Revolt and, instead, by annexing it, it prevented this "California nation" from becoming

my doubt: can we have the non parallel structure "rather than annexing" in option A correct? to what is "rather than annexing" parallel?