Nuclear triad
Israel is known to have nuclear-capable aircraft and land-base missiles, with the addition of nuclear-armed submarines this would mean that they now have a full triad of land-, air-, and sea-based nuclear delivery systems some of which would be invulnerable to a first strike by an enemy for the first time in their country's history. No other nation in the Middle East in known to be in possession of nuclear weapons, even though Iran, Iraq, Syria and Libya have started development programs that were never completed.
20th-century events
Since the 1940s there were concerns about the rising proliferation of nuclear weapons to new countries, which was seen as being destabilizing to international relations, spurring regional arms races, and generally increasing the likelihood of some form of nuclear war. Eventually, nine nations would overtly develop nuclear weapons, and still maintain stockpiles today: the United States, the Soviet Union (and later Russia would inherit these), the United Kingdom, France, China, India, Pakistan, Israel and North Korea. South Africa developed six crude weapons in the 1980s (which it later dismantled), and Israel almost certainly developed nuclear weapons though it never confirmed nor denied it. The creation of the Nuclear Non-proliferation Treaty in 1968 was an attempt to curtail such proliferation, but a number of countries developed nuclear weapons since it was signed (and many did not sign it), and a number of other countries, including Libya and Iran were suspected of having clandestine nuclear weapons programs.