The conflict has been compared to World War I in terms of the tactics used, including large-scale trench warfare with barbed wire stretched across trenches, manned machine gun posts, bayonet charges, human wave attacks across a no man's land, and extensive use of chemical weapons such as sulfur mustard by the Iraqi government against Iranian troops, civilians, and Kurds. The world powers United States and the Soviet Union, together with many Western and Arab countries, provided military, intelligence, economic, and political support for Iraq. On average, Iraq imported about $7 billion in weapons during every year of the war, accounting for fully 12% of global arms sales in the period. The value of Iraqi arms imports increased to between $12 billion and $14 billion during 1984–1987, whereas the value of Iranian arms imports fell from $14 billion in 1985 to $5.89 billion in 1986 and an estimated $6 billion to $8 billion in 1987. Iran was constrained by the price of oil during the 1980s oil glut as foreign countries were largely unwilling to extend credit to Iran, but Iraq financed its continued massive military expansion by taking on vast quantities of debt that allowed it to win a number of victories against Iran near the end of the war but that left the country bankrupt.