Starting with the advent of World War 2, DC's Earth would probably look radically different from our's.
Dozens of major cities and countries exist in the DC Universe that don't in our world.
Realistically, this Earth would be more technologically advanced from ours due to contact with alien races, ancient civilizations such as Themyscira and Atlantis, and access to super geniuses such as Ray Palmer and Lex Luthor.