In no particular order:
- Dismantling Mass Transit and Replacing Trains with Automobiles and Jets
- The widespread adoption of fossil fuel-based energy without a long-term sustainability plan
- The rise of nuclear weapons and the doctrine of Mutually Assured Destruction (MAD)
- The American Enterprise System & Maximizing Shareholder Value as the primary goal of corporations
- The mass production and global spread of single-use plastics
- Factory farming and industrialized monoculture agriculture
- The overuse of antibiotics and the rise of antibiotic resistance
- The re-interpretation of the Second Amendment from supporting the organized militia into an individual right to own guns
- The rise of planned obsolescence in consumer goods
- The deregulation of financial markets
- Mass surveillance and the normalization of privacy loss
- Neoliberal economic policies (a.k.a., Trickle-Down Economics) that broke unions and hollowed out the middle class while privatizing public services and cutting taxes on corporations and the wealthy
- Building neighborhoods where kids can’t play in the streets
- The military-industrial complex and the permanent war economy
- The rise of ultra-processed foods and the obesity epidemic
- The widespread use of asbestos in buildings and consumer goods
- Infusing information technology and personal computers with counter-culture libertarian ideology
- The ideological foundations of Fascism, Nazism, Zionism, Soviet & Maoist Communism, Segregation & Apartheid
- The War on Drugs and mass incarceration
- Gutting Mental Health Services & Housing
Dishonorable mentions that didn’t make the top 20, again in no particular order:
- The Red Scare & blacklists
- Choosing to use the naval propulsion reactor design as the basis of civil nuclear power generation
- Off-shoring strategic industries and the practice of arbitraging labor costs away from the consumer market
- Globalizing Just-In-Time supply chains and logistics management
- Post-Colonialism and the economic oppression and exploitation of the global South by development organizations and multinational corporations.
- Commercializing the Internet and authorizing the .com Top Level Domain
- Various failed attempts at map-oriented geopolitics in smokey back rooms like Sykes-Picot, Versailles, San Remo, Appeasement, Yalta, the Partition of India (Indian Independence Act 1947), the Partition of Palestine (UN Resolution 181)
- Commercial Airline deregulation
- Prohibition
- Americanization of the world
- Amu Darya river and Syr Darya river irrigation diversion that dried up the Aral Sea
- Recycling as a Public Relations initiative
- Infotainment, reality television, & talk radio
- Woodrow Wilson, The Birth of a Nation, the Daughters of the Confederacy, and the Lost Cause Myth
- The racism of people of European descent towards anyone who was darker skinned than them, while not conceived in the 20th century, continued to be widespread, but key elements in the US for the system of oppression based on race were decided in the 1890s. Notable decisions in the 20th century were the Immigration Acts of 1903, 1907, and 1918, which restricted immigration by country of origin, mental and physical capacity, and political beliefs, and Korematsu v United States, the case that legalized Japanese Internment.
- the 17th Amendment