North Vietnam by itself, no. The reason the US took such an interest in it, and fought a war costing thousands of lives, was because we were trying to limit the growing influence of communism via the USSR. The Vietnam War was part of the (not so) Cold War, one of many individual proxy wars influenced by the US and the USSR on one side or the other. The Soviets supplied the North Vietnamese and the North Koreans, while the US encouraged coups to put pro-capitalist dictators into power in various South American countries, and we supplied the Taliban with arms and equipment during the Soviet invasion of Afghanistan in the 1980s.

So in short, Vietnam itself didn't pose a threat to the US, but the growing influence of communism potentially did, which was why we tried to limit its spreading influence as best we could, while we ourselves spread the influence of capitalism (for better or worse)

As /u/onlysane1 suggests, even a united Vietnam presented little threat to the US, the wartime North still less so, except as an adjunct to one or other leading Communist power.

The big flaw in US analysis of the DRV as a strategic threat was that policymakers could never quite figure out which of the USSR or China - if either - a Viet Minh state might be an adjunct of. State Department studies on the eve of US military involvement saw no evidence of a Soviet proxy regime, still less a Chinese one, and through the 1960s Hanoi sought to maintain a delicate balancing act between the two powers as their relations cooled and briefly escalated into conflict, despite what with hindsight seems clear preference for Moscow.

It makes more sense to view the start of US entanglement in terms of regional instability in the aftermath of WW2, the weakening of the colonial powers and the emergence of Communist China. In the zero-sum mentality of much of the Cold War, any strengthening of Communist influence constituted a weakening of the US. In the event escalation brought its own heavy costs.