Because Castro had made public Guevara's "farewell letter" to him — a letter Guevara had intended should only be revealed in case of his death — wherein he had written that he was severing all ties to Cuba in order to devote himself to revolutionary activities in other parts of the world, he felt that he could not return to Cuba with the other surviving combatants for moral reasons, and he spent the next six months living clandestinely in Dar-es-Salaam, and Prague. During this time he compiled his memoirs of the Congo experience, and wrote the drafts of two more books, one on philosophy and the other on economics. He also visited several countries in Western Europe in order to "test" a new false identity and the corresponding documentation (passport, etc.) created for him by Cuban Intelligence that he planned to use to travel to South America. Throughout this period Castro continued to importune him to return to Cuba, but Guevara only agreed to do so when it was understood that he would be there on a strictly temporary basis for the few months needed to prepare a new revolutionary effort somewhere in Latin America, and that his presence on the island would be cloaked in the tightest secrecy.