It Goes Back to a 1991 Deal

Apple moved into Ireland in 1980, building infrastructure and jobs for ten years before they attempted to use their position to negotiate a better deal. Which they did, Business Insider explains:

What It Means

This is the largest amount that the EU has ever ordered a company to pay, which makes the ruling precedent-setting. The closest amount was $1.6 billion requested from French energy giant EDF in 2015. It’s illegal for a government in the EU to strike a so-called “sweetheart deal” with a company. The European Commission classes those deals as illegal state aid, and it has decided that Ireland’s deal with Apple is exactly that.” Apple says that the deal could affect how it invests across Europe and the number of its employees in Europe. Apple also stated that they would contest the ruling, and that they were “confident the decision will be overturned.”