I remember Brasilia being built because it was not only in the main news in the United States, but there was a story about it in Our Weekly Reader, which was a sort of newspaper for elementary school children.
I'm not sure what the capital was previously. I assume it was Rio de Janeiro because... I hate to say it... it's almost the only Brazilian city that people in the United States know. It was the biggest city in Brazil then, and I only learned this year that Sao Paulo is bigger today.