Here's an interesting search hit, apparently from some media company. I hope they found what they were looking for.
9x18 Makarov is nothing "American." It's just 9x18 Makarov.
The "9" is roughly the diameter of the bullet in millimeters. The "18" is the length of cartridge case in millimeters. It is intermediate in power between the .380 ACP (also known as 9x17) and the 9mm Parabellum (also known as 9x19).
Sometimes I wish they would just send an email and ask. I would be happy to supply any information I could.