US Dept of Justice to charge Walmart with Bribing Mexican Officials

My question is why is Walmart in this case when the US government is bribing North Korea with food to stop their Nuke program? Walmart was paying for influence just as people and companies make a political donation to gain influence with the people in power. What is the difference between Walmart bribing a Mexican Official and donating to the Campaign of Mr XYZ? Both are a payment in the hope of getting something.