In foreign policy, he initially sought an alliance of Nordic countries, but without success, instead maintaining strict neutrality while building up among the most impressive armed forces in the world (surpassed only by the United States, the Soviet Union and Israel in terms of per-capita spending), making the Swedish Air Force the third largest in the world, while ultimately rejecting nuclear capability, signing the nuclear non-proliferation treaty in 1968. Erlander's mandate coincided with the post–World War II economic expansion, in Sweden known as the record years, in which Sweden saw its economy grow to one of the ten strongest in the world, and subsequently joined the G10.