People have known how to make very large bombs for a long time (e.g., in 1961, the USSR tested a bomb with a yield of 50–58 megatons) so it says something that

People have known how to make very large bombs for a long time (e.g., in 1961, the USSR tested a bomb with a yield of 50–58 megatons) so it says something that for decades, no military has had any bombs larger than about 1.3 megatons.