What historical evidence can be found to support the belief in Alexander the Great's conquest of much of the Middle-East?

Beyond the written documents put down years after his conquest which still exist, the Hellenistic civilizations that dotted the Middle-East after the conquest testify to the reality of Alexander's conquest. These successor states had a great effect on the civilizations that they came in contact with including the Persians, Jews, and Egyptians to name a few.

How did President Polk justify the declaring war on Mexico in 1846?

The border of Texas was being disputed by the Mexicans and Texans at the time but Polk placed troops in the contested area anyway. When American forces were fired on in the contested land between the Rio Grande and the Nueces rivers, Polk declared that "American blood had been shed on American soil," and asked Congress to declare war.

How did the Treaty of Versailles contribute to causes of WWII?

The Treaty of Versailles assigned war guilt exclusively with the Central Powers, most notably the Germans. War guilt came to mean that the Germans would have to pay reparations to the Entente Powers and that they would lose a good deal of territory to the formation of new states in Central Europe. Right Wing German Nationalists used this and the financial crisis of 1929 to appeal to German pride to gain power. The Nazi's also started to take the land they had lost back little by little and the allies allowed it in part because the Versailles treaty had been so harsh.