How does the constitution improve upon the weaknesses of the articles of confederation?

The United States Constitution of 1789 provided a strong union between the sovereign states. The first Articles of Confederation in the United States needed a new president elected yearly, and had little to no cohesion between states. This meant that states were often at conflicts with eachother, sometimes bloodshed, business between states was difficult because of the different currency for each state. And forming a formidable Navy was just about impossible, also the national military as a whole was short supplied in general. This all and more, was fixed with the adoption of the United States Constitution in 1789.

because the vietnam war was fought in an especially brutal and untraditional way