@Vincenzo -- You mean nations like those in the Middle East that are using the money we pay for oil to attack us? It would be great to not trade with those countries but there's a problem with that. Namely, we need their oil to keep our economy going while we don't need Cuban cigars. In other words, issuing sanctions against some nations is easier than issuing sanctions against others and how fair is that?
On the other hand, there is some real evidence showing that sanctions were harmful in the case of Cuba. The biggest export from Cuba is sugar, and we refused to buy it after the country went communist. Ah, but the Soviets were more than happy to purchase that sugar and that drove Cuba deeper into the Soviet camp. Sanctions may have backfired in that case.
Oh, and let's not forget the negative impact that sanctions have on American businesses. Once upon a time, Cuba and Iran were among the largest purchasers of rice grown in the United States. When we refused to trade with those countries, that hurt a lot of American farmers.
Sanctions are tricky things to deal with politically and may or may not be effective.