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
Fascist - Following fascism, a set of ideologies that advocates dictatorial power, political violence, suppression of opposition, traditional gender roles, and official racism.
Nazi Germany - The German state between 1933 and 1945, when it was ruled by Adolf Hitler's Nazi party.
Axis - During World War Two, the Axis powers were a military coalition that opposed the Allies. They included Germany, Italy and Japan.
The Allies - During World War Two, an international military coalition including the UK, USA and the Soviet Union.
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.
Consulate - The office in a foreign city where government officials work and look after their citizens in that country.
Atom bombs - An atom bomb rapidly releases nuclear energy.