Depends on what you define as civilization (are America and Brazil part of the same Civiilization)? But entire continents (S. America and Africa) would be enti

Depends on what you define as civilization (are America and Brazil part of the same Civiilization)? But entire continents (S. America and Africa) would be entirely untouched by direct attacks. The only risk of total collapse is deep and long nuclear winter. Even in that event (which I don't really think is realistic) coastal areas would fare better.