Final answer:
The nickname for US soldiers during WW1 was "Harlem Hellfighters" for the 369th US Infantry, an African American regiment celebrated for their valor and awarded France's Croix de Guerre.
Step-by-step explanation:
The nickname for US soldiers during WW1 varies, but a particularly notable one was "Harlem Hellfighters". This nickname was given by German troops to the members of the 369th US Infantry, an all-African American regiment that fought valiantly alongside the French army. Despite facing high casualties, their extraordinary bravery was recognized with France's Croix de Guerre, one of the nation's highest military honors. The bravery and service of the Harlem Hellfighters exemplify the courage and sacrifice of US soldiers during World War I.