A. Violent attacks form the Eastern tribes even led to the downfall of Rome, as soon as the mongols got to Rome they had no challenge in defeating such a weak nation in it's decline.
Answer:
Constitutional amendments.
Explanation:
The first method authorizes Congress, "whenever two-thirds of both houses shall deem it necessary", to propose Constitutional amendments. ... It moreover equally enables the General and the State Governments to originate the amendment of errors, as they may be pointed out by the experience on one side, or on the other.
Answer: Tanks and military-grade planes
Explanation: Imperialism was about almost everywhere in Europe at the time and around that time most European countries had territories in Africa which lead to constant fighting for the land there. What this lead to was intense fights between nations by them creating proxy wars (militias/Rebel groups) to fight against each other which were being supplied by that country that wants more land for them self. With that it lead to Archduke assassination which lead countries to declare wars on one country which then would mean they would declare war on multiple countries in realty because countries would ally each other and the domino effect went down hill from that. So Archduke assassination was just really a "reason" to fight with another nation for more land (resources).
I think 21 to 35 because i think that age is about the time were they start to become lazy and don't car about things the much. <span />