Are Americans ever justified in breaking the laws of their country?
Laws are put in place for our protection and the protection of others. There are laws that govern our conduct, laws about paying taxes, and laws that protect property and life. But if these laws conflict with the personal beliefs or desires, are we required to follow them? If they conflict with God's law, no.
God's law is based on two principals: you should love God with your whole heart, soul, mind, and body; and you should love our neighbor as yourself. If you adhere to this, then you follow the laws of the United States. You would not take something that did not belong to you; you would respect all people no matter what race or sex, and you would make sure to be honest in all things - this includes the paying of taxes. But, if the time came when the law of the country conflicted with the law of God, then I would have to obey the law of God.
A law that would allow people to won someone else, or one that would allow a group of people to be taken from their home and moved somewhere else less inviting and with less resources would also be an example of a law that should not be obeyed. We are all created the same, and we all should be treated the same. God never intended for one group of people to dominate another group of people and impose their beliefs and values on another human being.
The laws of the United States are based on the premise that all men are created equal, but at times men forget this. When they forget this, then laws are made that are not in harmony with God's. Be it laws that make separate but equal, or a law that removes a group of people from their homes, or a law that forces one to go to war, when they conflict with God's law, then I can no longer obey them. As Peter said in Acts 5:29, "We must obey God as ruler rather than men." That is what I do.