The north had better equipped weapons than the South
Let me handle your first question -- always good to do one question at a time here. :-)
Prior to President Theodore Roosevelt, those who preceded him in federal government had tended to side with industry leaders, expecting laborers to fall in line and do the work for the good of the companies. In 1902, when there was a particularly tense strike by coal workers, Roosevelt invited both sides (labor leaders and management leaders) to the White House to negotiate. This was an example of the way he saw the role of government leadership as "steward" to the nation, mediating on behalf of everyone's interests, not just the interests of a powerful small group. His "Square Deal" policies were aimed at making things fair and square for the general public. An example of this would be how much land was set aside under his administration as national forests, national parks, national monuments, etc. He was seeking to protect the use of the land for all Americans' interests, rather than letting corporations tear into any land or forest they wanted in order to grab natural resources.
Cyrus' conquest was relatively humane compared to empires preceding his, such as the Babylonians and Assyrians. He allowed many areas of his empire a great deal of autonomy, rather than centrally controlling things. This distributed leadership allowed Persia to cover a greater geographical area than previous empires in that era and still be fairly stable, since most of its subjects were content to remain under Persian rule. Persian law was more codified and less arbitrary than previous empires; the king's seal declared approval of law which could only be reversed by further approved decrees -- not quite rule of law but going in that direction.
