Final answer:
Ambrose Bierce, an American journalist and writer, went to Mexico to report on the Mexican Revolution but disappeared without a trace.
Step-by-step explanation:
The writer who went to Mexico to report on the Mexican Revolution but never returned to the United States, and all trace of him disappeared, was Ambrose Bierce. Bierce was an American journalist and writer who ventured to Mexico in 1913 to witness and report on the revolution. However, after entering Mexico, he vanished without a trace and was never seen or heard from again.