Leonidas, one of the two kings in the Spartan diarchy, died fighting the Persian Invasion at Thermopylae. He had a force of three hundred Spartans, augmented by a thousand or so soldiers from his allies. He had sent the main part of his force in retreat, and was holding the pass at Thermopylae in order to give the Athenians and the other Grecian states more time to prepare against the Persians. <span />
Beavers might be the most well-known animal architects, and with good reason. These prolific builders fell trees and gather sticks and mud to construct dams, which create ponds that offer predator protection and easy access to food during the winter.
Answer:
1. War and insecurity 2. Economic crisis (poverty) 3. Overpopulation
Explanation:
1. War and insecurity - as example Syrian crisis and war against ISIS
2. Economic crisis (poverty) - mass immigration from Poland to USA in the late XIX and early XX century.
3. Overpopulation - mass immigration to Europe from African countries in the last few decades.