Historical Significance
Then
Because of the tensions between allies in the Cold War, the U.S. had to make quick decisions, so first looked at the fact that World War II just ended and it was highly unlikely that a state of peace would emerge and stay, so when asked by Britain, Belgium, The Netherlands, and Luxembourg to join their “defensive alliance” in 1948, they decided to sign with no hesitation. They signed because they knew this would be one step in the right direction towards creating and keeping peace not just in the United States, but worldwide.
Making allies with other countries especially in a time where revenge and concern clouded many citizens' minds of Germany, proves that the U.S. was willing to accomodate when needed instead of staying on the outskirts. The significance this friendly comradery had on the Airlift was proven when they were able to come together and ultimately defeat the Soviets by outsmarting their plans and trusting each other.
Source: Khan Academy
Now
Because of the Berlin Airlift, various treaties and acts were implicated to help better prepare and handle large international ordeals in the future.
During the Airlift, the treaty made between Britain, Belgium, The Netherlands, Luxembourg, and the United States was named NATO (North Atlantic Treaty Organization), which is still operating;
however now consists of 28 members. NATO “promised” that any sort of attack or threat to one of the members would exasperate all of the other members. Due to this, NATO soon was recognizable as the “major international body opposing communism” in the twentieth century.
Source: Quartz
Since creating this treaty, it has become essential to the United States as well as the other countries involved in "safeguarding the freedom and security of all its members by political and military means.” Today, the United States refers to NATO as its “most important alliance” because of certain scenarios when they were in need of help such as in New York during 9/11. Almost immediately after the U.S. was attacked, the Canadian and European ambassadors of NATO contacted a U.S. ambassador to let them know their governments were willing to come to their defense. Those countries made it clear that day that when there was an attack on the United States it was an attack on them as well. NATO wasn’t just created for the Berlin Airlift, but for centuries to come.