Although your question is broad and can be applicable to many situations throughout history, it especially hits home for the Space Race and the Cold War. The simple answer to your question is: it depends! I think it depends on who you ask; an economist may say war profiteering or the promise of financial gain in the public and private sectors, a sociologist may say public misinformation and fear mongering, and an amateur aviation historian may say those [big] (https://www.fas.org/nuke/guide/russia/bomber/tu-95-bear_p4.jpg) [beautiful] (http://upload.wikimedia.org/wikipedia/commons/2/21/Soviet_M-4_Bison_bomber_in_flight_1982.JPEG) [bombers] (http://upload.wikimedia.org/wikipedia/commons/5/5a/Convair_B-36_Peacemaker.jpg)!!

At the beginning of the Cold War, the American, British and French forces began carving up Western Germany, while the Soviet's began carving up Eastern Germany. We have to remember one of the first "battles" of the Cold War: the Berlin Airlift. Beginning on June 24th, 1948, General Curtis LeMay (remember this guy, he's important for later) orchestrated what became one of the largest and most successful humanitarian airlifts in history. The success of the airlift is multifaceted; it didn't just demonstrate American and British dedication to containment and their collective logistical prowess. It was a propaganda victory for the Allies, especially for the American Air Force. In fact, [certain aspects] (http://www.pbs.org/wgbh/amex/airlift/peopleevents/p_halvorsen.html) of the airlift were purposefully carried out for propaganda purposes. More importantly, the airlift showed that when tanks and soldiers failed, aircraft could get the job done. We'll revisit this idea in a little bit.

The Berlin Airlift all happened under President Truman, who took over the presidency from FDR after his death in 1945. The situation that Truman inherited was truly unique: he was the Commander in Chief of one of the largest and technologically superior militaries in the world, with the most powerful weapon in the world at his disposal. His eventual use of the atomic bombs to end the war solidified the American Air Force as a dominant power on the world stage, and as a dominant power in the American military machine. Unlike President Roosevelt, whom Stalin considered a skilled politician, President Truman was viewed by many of his contemporaries as a "pushover" (Stalin, in fact, remarked that he found Truman "neither educated nor clever") and the American military machine was quick to test this perception. Militarily, we can see this when Truman decided to fire General MacArthur for what ultimately was insubordination. Politically, we can see this during the political circus that defined the McCarthy era.

Truman's successor, Eisenhower, was sworn into office just as the Cold War began to heat up. The office that Eisenhower inherited was desperately in need of someone with an unyielding personality, who could calmly handle stressful situations. During his first term, he saw an end to the McCarthy era of fear, and threatened nuclear war with China in order to end the Korean War. Although Eisenhower, Truman, and Roosevelt all opposed the spread of Communism, Eisenhower knew that funding a conventional military in order to defeat the Russians would bankrupt the United States, and the resulting US military buildup would still be a fraction of the size of the Soviet military. Thus, Eisenhower's strategy was one of nuclear deterrence: combat the spread of Communism by threatening to use nuclear force. This plan had the dual benefit of maintaining the harsh stance on Communism while being fiscally conservative with the defense budget, which was spinning wildly out of control. The only practical method of carrying out the military implement of Eisenhower's "New Look" policy was the use of a superior bomber force, which was headed by... General Curtis LeMay of Strategic Air Command. Once again, a superior air force offered a solution to tanks and soldiers.

So this puts Eisenhower in a bit of a difficult situation. On one hand, Eisenhower recognizes the need for a strong bomber force, capable of carrying conventional nuclear payloads that can be used in the case of nuclear war. The Air Force Chief of Staff knows this, and demands an exorbitant amount of money to fund ridiculous proposals (such as [nuclear powered aircraft] (http://en.wikipedia.org/wiki/Aircraft_Nuclear_Propulsion), that spew radioactive air out of their engines). In the meantime, the other branches of the military are trying to siphon money off for their own "ridiculous" proposals (such as this [ridiculous army project] (http://en.wikipedia.org/wiki/Redstone_rocket) that almost never got off the ground, and this [ridiculous navy project] (http://en.wikipedia.org/wiki/George_Washington-class_submarine) that threatened to sink itself.) And Eisenhower would have probably considered a lot of these requests, had he not already put money on this [ridiculous CIA initiative] (http://en.wikipedia.org/wiki/Lockheed_U-2) that was sending him real time intelligence on the actual size of the Russian military buildup.

And then, [this article] (http://thespacereview.com/article/576/1) came out. This fueled a public panic, which caused Congress to hold public hearings on how Soviet scientists and engineers had bested the Americans. Although this specific instance turned out to be a hoax, this was a very real fear a year before when the Soviets launched Sputnik. As a response to this article, the Air Force generals started beating down Eisenhower's door, asking for funding so that they could combat this new wonder weapon that "they were absolutely positive" was being produced in the hundreds, which resulted in the "bomber gap." Eisenhower, who was being kept up to date by CIA Director Allen Dulles and with the ongoing U2 overflights, knew that there was no "bomber gap," but couldn't tell the public why. This ongoing battle between the public, the Air Force, the Russians, and Eisenhower continued through the latter half of Eisenhower's presidency, and was a major factor in Eisenhower's speech regarding the military industrial complex.

During Kennedy's election campaign in 1961, Kennedy was a huge proponent of closing the "bomber gap" which was still a wide concern at the time. Once he got into office, and began receiving actual reconnaissance from U2 overflights, even he recognized that there was no "bomber gap." However, Kennedy's presidency was filled with "hot spots" such as the Cuban missile crisis, the Bay of Pigs Invasion, and the capture of Francis Gary Powers, all of which increased the possibility of global nuclear war.

So, how does all of this relate to your question? I've tried to show that the Arms Race in the Cold War was not due to a single event, but rather was the result of a number of complex world events. The spread of misinformation, fear, and an attempt to limit the spread of communism while saving money all played a significant role in the Arms Race.