A common point is that during both periods, the United States focused on expanding our involvement in global affairs, just into different regions. In the early 20th century, we became more directly involved in the European and Pacific theaters. In the 21st century, our focus has been more oriented towards the Middle East (specifically Iraq, Iran, and Afghanistan), due to the War on Terror and our role as global hegemon.
In the first part of the 20th century, the US gradually shifted our foreign policy from an isolationist strategy focused exclusively on the Americas to becoming far more directly involved in European and Pacific affairs. Our victory in the Spanish-American War in 1898 ultimately brought us control of the Philippines and set us on a course for war with Japan in World War II, as the Japanese sought to dominate the Pacific during this time. The construction of the Panama Canal in the early 20th century further cemented our intentions to dominate commerce in the Americas and expand into Pacific markets.
Our participation in World War I saw us get directly involved with European affairs for the first time, and Woodrow Wilson's failed attempt to establish a League of Nations set a precedent for the kind of relationship we would ultimately have with Europe and the rest of the world decades later. Our involvement in World War II firmly ended our isolationist foreign policy, and instead saw the United States replace Great Britain as the global hegemon. The newly established United Nations keeps us firmly involved in global conflicts, and as the world's hegemon, we shoulder the majority of the burden in UN "peacekeeping" activities (Korean War, Vietnam War, Gulf War, etc.).
In the 21st century, our direct involvement has been focused on the Middle East. After the 9/11 attacks, we launched a campaign of retribution in Afghanistan against Al Qaeda and the Taliban, with mixed results. In 2003, we became directly involved in Iraq for a second time (after the Gulf War in the early 1990s), overthrowing Saddam Hussein's regime. And after those campaigns concluded, most recently we aided Israel in their attack on Iran's nuclear facilities. Iran has been an enemy of the United States since their revolution and overthrow of the shah in 1979. In the aftermath of the Cold War, China has replaced Russia as our primary geopolitical adversary. Our broader foreign policy has shifted towards maintaining our status as global hegemon against a loose alliance of China, Russia, Iran, and their proxies. We have attempted to bolster our position with strategic alliances with nations such as Israel, Saudi Arabia, Japan, South Korea, Vietnam, India, and the Philippines. The strength of these coalitions will be tested if China tries to invade Taiwan.
Another common point across both time periods is our direct involvement in the global oil market. In 1941, our embargo of Japan cut their access to oil and crippled their economic and militaristic ambitions, leading to them declaring war on the US with the attack on Pearl Harbor. In recent times, we have attacked the Houthi rebels in Yemen, due to their frequent attacks in the Persian Gulf disrupting the flow of oil and other commodities in the global trade network.