Numerous parallels can be be made today.
Was just helping my daughter with her history (Revisionist crap). One of the essay questions was compare and contrast the Vietcong victory in Vietnam with the Iraq war?
I had to explain to her that after Tet, the VC weren't really a factor. And after the NVA took over the south, the VC was dissolved (most of them were northernors by this time anyway), and southern communists were taken out of power on the chance that they had been tainted by living in the south for so long.
Nixon began to withdraw combat troops immediately upon being sworn into office and before the war had been won, The North Vietnamese continued to test our resolve with massive conventional force invasions. I was personally involved in the attacks across the borders in the Central Highlands in 1971. The biggest attacks occurred in 1972, when all our grounds forces had either left the country or withdrawn to coastal enclaves.
Through the course of these offensives, we continued to withdraw ground troops demonstrating our unwillingness to stand up to outright invasion. The South Vietnamese were able to stand up against these attacks with American air and artillery support, but soon even these units were gone, the Paris Accords were signed and all that was left was a promise to provide financial and military logistical support.
When the 1975 invasion started, the Democrat Congress refused to deliver on the United States promise. But, without American forces, the South Vietnamese had insufficient forces to stop a multi-corps armor and infantry invasion.
The North Vietnamese won the war with conventional forces fighting conventional tactics in an undeveloped country. We did the same thing in the South Pacific in WWII. The South Vietnamese were left to defend their country with what little they had, much like Japanese forces in the Pacific.
Certainly, if the Congress had lived up to our promises, the South Vietnamese could have held out longer, but they almost certainly couldn’t have won.