I don't know how you define "last startup to succeed", but... Hummer (1992, 28 years ago), Pagani (1992), McLaren (1985, 34 years ago), Kia (1974, 45 years ago), Hyundai (1967, 52 years ago) and even Jeep (1946, 74 years ago) and Saab (1945) seem like they would qualify as well?
Hummer and Jeep both had their original vehicle designs funded by the US military. None of the rest of those are US companies.