The causes of U.S. port congestion in 2020-2021 are mainly caused by multiple factors, related to the COVID-19 pandemic, supply chain disruptions, and surge in consumer demand. The following is a simple cause and effect analysis:

Causes:

1. Pandemic:

• The COVID-19 pandemic in early 2020 caused factories around the world to shut down, especially in manufacturing centers in Asia, and the supply chain was temporarily disrupted. This resulted in many goods being unable to be produced or shipped as scheduled, and logistics was severely affected.

2. Sudden Increase in Demand:

• As time at home increased during the pandemic, American consumers' consumption patterns changed. Demand for home-related items such as furniture, electronic products, and sports equipment surged, and imports increased rapidly.

3. Labor Shortage in Ports:

• The pandemic has left the port with a shortage of workers, truck drivers and warehousing personnel. Many workers are unable to work due to infection or pandemic prevention measures, resulting in a reduction in port handling capacity.

4. Shortage of Shipping Containers:

• At the same time, there is a global shortage of containers and ships, as many containers are stuck in ports and cannot be turned over in time, resulting in a significant increase in shipping costs and time.

Consequences:

1. Port Congestion:

• Major U.S. ports, especially those of Los Angeles and Long Beach, have become the worst congestion zones, with ships queuing to unload and even weeks of delays. The volume of cargo handled by these ports once reached its limit, causing logistics bottlenecks.

2. Global Supply Chain Delays:

• The port congestion has been accompanied by delays in the global supply chain. Many manufacturers have been unable to obtain raw materials in time, and retailers' supply of goods has also been affected. There have been shortages in the supply of everything from auto parts to electronic products.

3. Price Increase:

• Rising transportation costs and supply chain disruptions are exacerbating supply shortages, further pushing commodity prices higher. Consumers are facing more product shortages, which is also putting pressure on inflation.

4. Government Intervention:

• As port congestion and supply chain issues continue to impact the economy, the Biden administration has stepped in, announcing an extension of port operations to 24 hours and seeking solutions to relieve these bottlenecks.

Overall, the port congestion problem in 2020-2021 reflects the fragility of globalized supply chains and highlights the profound impact of the pandemic on the global economy and logistics system.