Complex sentence: On the contrary, it seems to be downplayed by saying that Rosas didn't break relations (should he?), like if nothing happened in that field from 1834 to the mid 20th century.
Split into simpler sentences: On the contrary, it seems to be downplayed by saying simply that Rosas didn't break relations (should he?). Like if nothing happened in that field from 1834 to the mid 20th century.