The Clankers are the countries (and their citizens) who use high-tech machines instead of bio-engineered creatures. Walkers are used for land battles with Darwinist creatures and enemy troops, and zeppelins are used to battle Darwinist airships like the Leviathan. The Clankers also have ironclad ships equipped with kraken-fighting arms.
The real-world counterparts of the Clankers are the Central Powers. Alek believes that the Clanker powers are the ones responsible for his parents' deaths, and for starting the war. At the end of the series, the Clanker powers seem to be losing the Great War.
The Clankers do not seem to be on friendly terms with any of the Darwinist Powers, even when they are not at war, as the Clankers view the Darwinists' fabricated animals as a violation against God, while the Darwinists dislike the nature of machines. Some countries use both Darwinist and Clanker technology, such as the United States, Mexico, and Japan.