After the establishment of the IDF the two Jewish underground organizations the Etzel and Lehi joined with the IDF in a loose confederation but were allowed to operate independently in some sectors until the end of the 1948 Arab-Israeli War, after which these two organizations were disbanded, and their members integrated into the IDF. The modern IDF came into existence during the period from 1949 to 1956 by experience gained through regional conflicts with their Arab neighbours. From 1956 to 1966, the IDF faced less conflict and used this time to purchase new equipment and change from an upstart army to a professional fighting force. As well, this period allegedly saw Israel develop its nuclear capability. Following these developments, the IDF increasingly emerged as one of the most powerful and modern military forces in the world.