How did Alexander the Great attempt to unite his empire? How does the United States reflect that attitude today?

He attempted to unite them by beginning with the unification of all who had the same, Greek, culture, and then allowing all countries that he conquered to keep their religion and customs and keep doing whatever they would normally be doing, which made people respect him instead of fear and hate him. The US accepts all people and their religions and their beliefs giving all people equal rights and equal treatment, even those that are in war with them.