The greatest threat America faces today is nationalism, which seeks to rule through intimidation of "others": other nations, undocumented people in America, and people seeking to enter the country.
A particularly dangerous threat now is the taunting of North Korea by President Trump. In the past, nationalist movements by Hitler, Hirohito, and Stalin led to World War II and the Cold War.
The nationalist sentiment in America today is fueled by the frustration and hopelessness of citizens who are unfairly left behind, in spite of their efforts, while a privileged few live in luxury and other people seem to be receiving unearned handouts. The root cause of American's frustration is unregulated free-market capitalism and our income tax system.
America thrives on entrepreneurship, which requires private ownership of businesses and the profit motive. The tax system must not thwart its entrepreneurs. At the same time, large publicly-traded corporations must be regulated, to curb excesses and to assure that externalities, such as environmental protection, are taken into account.
The federal tax system must be fair to everyone, while our government collects enough revenue to fund essential public services: infrastructure, universal healthcare, public education and the safety net for the disabled and disadvantaged people of all ages. And it must not keep growing the national debt. Paying our taxes is a patriotic act, along with military service, public service and basic honesty.