Barbed wire

Barbed wire was a cheap, simple anti-infantry barrier used by Soviet forces during the Great World War II. It was generally ineffective at impeding the progress of anything larger than light vehicles. After the war, difficulty with handling the wires, and the general ineffectiveness of the barriers, led to the abandonment of barbed wire as a military barricade, though civilian farmers would use it as an inexpensive way to keep their livestock in check.

Description
Barbed wire, was, as it's name implies, a length of steel wire with razor-sharp barbs protruding at intervals throughout it. Infantry crossing through a barbed wire fence would likely risk severe lacerations, and light vehicles would certainly have their tires cut open. While it would be possible for an infantryman to slowly and carefully negotiate his way through the wire, or cut the strands of wire to pass, in the heat of battle this would endanger their lives. Therefore, infantrymen and light vehicles were trained to avoid the barbed wire. However, infantry armed with explosives found that, luckily, their weapons could clear a path through the barricade.

Strengths
Barbed wire was extremely cheap, and could impede certain varieties of enemy infantry.

Weaknesses
Despite being half the cost of concrete walls, barbed wire was a great deal less effective. Explosives could easily poke a hole through the defense, and tanks and other tracked vehicles could just drive over it without fear. Also, since barbed wire was low to the ground, it would not serve as decent protection against even direct-fire weapons, like tank cannons.