Career leadership at the State Department have resigned en masse since the appointment of Rex Tillerson. These are career officials, and not political appointees. The size of and suddenness of resignations that are unusual. From the Business Insider article linked prior:
Former State Department officials and foreign-policy professionals who spoke with Business Insider said that there is typically a high degree of turnover when new administrations are installed. But they all said that the abrupt and simultaneous exodus of senior management officials was unlike anything they’d seen before.
“This is unusual because it seems to be hitting the management folks, who are the skeleton of what delivers our foreign policy in the field,” Ambassador Richard Boucher, who served as State Department spokesman for Colin Powell and Condoleezza Rice, told Business Insider.
“These are the people who maintain the embassies and ensure diplomats’ security around the world, vet visa applicants, et cetera,” Boucher said.”They’re the support apparatus the administration has to go through if they want their new policies to be delivered and implemented.”
Eliot Cohen, a top official in George W. Bush’s State Department and a professor at Johns Hopkins University, told Business Insider that he had “never heard of anything like this before.”