1. Depends on the method of destruction. Does this mean to cause an explosion so massive it consumes the entire area or actually destroy the entire landmass of the continents?
If the former:
A rough diameter of the USA (East Coast to West Coast) is 4626.145 kilometers. We cut this in half to find the Radius.
4626.145 = 2313.0725 km
The formula for non-nuclear explosions is:
2313.0725 = Y^(1/3)*0.28
R = 2313.0725 km
Y = 563,759,199,696.200684 KT
Or 563 Teratons. Large Country level+
If the ladder:
The land area of mainland USA is 7,663,941.7 km^2 and has an average elevation of 0.76 km
Volume = Area * Elevation
7,663,941.7 * 0.76 = 5,824,595.692 km^3
5,824,595.692 * 1e+15 = 5.8245957e+21 cm^3
Assuming Fragmentation:
5.8245957e+21 * 8 = 4.6596766e+22 J
11 Teratons. Country level
2. The Gravitational Binding Energy of Mars is 1.144 Zettatons. Which is Small Planet level like Cross said.