Millionaire fashion designer
I would go with 'Major sandstorms destroyed the crops' because the Indus Valley civilization most likely declined by something affecting the food.
The four main causes of WW1: "M.A.I.N"
Militarism: build up of military might (created tensions of war)
Alliances: agreements of European countries to help if war came (more tensions)
Imperialism: with European powers expanding their reach to new lands (this created a global competition for power?
Nationalism: extreme amounts of pride for your country (competition to be the best)
Im not 100% sure.. but im willing to say it's the 19th amendment?