Eric Margolis writes:
Iran and Israel, both hostile to their Arab neighbors, became very close allies, to the fury of deeply religious Iranians and the Shia clergy, which strongly supported the Palestinians. The Shah even negotiated to buy Israeli missiles with nuclear warheads in exchange for a steady supply of oil. Washington offered to sell Iran 26 nuclear reactors.
The US, Britain, and the oil Arabs financed and helped arm Iraq. Israel sold Iraq a reported $5 billion in US arms and spare parts. Europe supplied Iraq with chemical weapons, food and arms.
Supply them with the same weapons you later invade them for. Excellent way to keep the military-industrial complex happy.