Are we back to the 1930s? Twice in the last century, regional tensions ended up setting a fire under a complex web of global alliances and dragged the whole world into war.
War warning on day missile hits US cargo ship
Vital decade: Grant Shapps says the world order has been "shaken to its core". Glossary
Yemen - The poorest country in the Gulf region is in the midst of a humanitarian crisis.
Houthis - An Islamist rebel group that controls a large part of Yemen. They are allies of Hamas in Gaza.
Cargo - Goods that are being transported.
Consulate - The office in a foreign city where government officials work and look after their citizens in that country.
Iran - A country in Western Asia, officially called the Islamic Republic of Iran. It has a population of 84 million.
Proxies - In warfare, a proxy is a smaller military power that fights or otherwise acts on behalf of a larger one.
Atom bombs - An atom bomb rapidly releases nuclear energy.