Soon after taking office, President Nixon introduced his policy of "vietnamization" due to the unexpectedness of the Viet Cong’s Tet Offensive. The plan was to encourage the South Vietnamese to take more responsibility for fighting the war. It was the US’s intention that this policy would eventually enable the US to withdraw gradually all their soldiers from Vietnam. The South Vietnamese passed a law that called up into the army all men in South Vietnam aged between seventeen and forty-three. In June, 1969, Nixon announced the first of the US troop withdrawals. The 540,000 US troops were to be reduced by 25,000. Another 60,000 were to leave the following December. Nixon's advisers told him that they feared that the gradual removal of all US troops would eventually result in a National Liberation Front victory. It was therefore agreed that the only way that America could avoid a humiliating defeat was to negotiate a peace agreement in the talks that were taking place in Paris. In an effort to put pressure on North Vietnam in these talks, Nixon developed what has become known as the Madman Theory. Bob Haldeman, one of the US chief negotiators, was told to give the impression that President Nixon was mentally unstable and that his hatred of communism was so fanatical that if the war continued for much longer he was liable to resort to nuclear weapons against North Vietnam.