1. Brazil
The fastest route to second citizenship via naturalization is in Brazil. Marrying a Brazilian national will not automatically grant you citizenship. It will take some paperwork and proof of one year of marriage to submit the official application for naturalization. You will not have to give up on your first citizenship once you get the official status of the citizen of Brazil. Moreover, if you like traveling, there are many advantages to having Brazilian passport. It offers a visa-free travel even to Russia.
We hope that our list of the easiest automatic citizenships to obtain by marriage was helpful and informative.