The Strait of Hormuz, through which 21 percent of the world's crude oil has to pass, is extremely important for the global economy. If Iran decides to disrupt or even completely stop shipping traffic here, it could trigger a global crisis.
All merchant ships that want to enter or leave the Persian Gulf must pass through this strait. Asia would be most severely affected, as these countries get 80 percent of their oil from this very region. Iran itself also has to transport its own oil through this road and is dependent on the income from the oil trade. However, if the US and its allies decide to impose stricter sanctions on Iranian oil than before, Tehran would have nothing to lose. If new oil sanctions are not imposed, Iran will not cut off its most important source of income. Iran can use this leverage to cause oil prices to skyrocket. It is enough to stop a few ships on their way. But if the Western allies actually want to restrict this very source of income that Tehran uses to finance terrorist groups such as Hamas and Hezbollah.