Recent scholarship from the excavation of Mothership Zeta after its captain, Sally, started to allow Super-Mirelurk/Enclave scientists onboard, that perhaps it was Aliens that inticed the start of the first nuclear waepons fired.
It was the United States of Russia. Contrary to what Gerance would try to say, it is accepted that among many historians that the USOR was the first one to enter the unlock code on the 8th Generation iNuke and tap the button.