What north vietnamese tactics made it difficult for u. s. troops to defeat them?

The North Vietnamese military (also known as the Vietcong) tactics made it difficult for the United States to defeat them because:

A) They did not wear uniforms- This made it challenging for the United States military to differentiate between who was a citizen and who was a member of the Vietcong.

B) Ambush/Hit and run style of fighting- This military style of fighting can be seen as unpredictable and random. This makes it so that the US military has to be on high alert at all times.