In an exception notice filed yesterday, the Federal Communications Commission will now allow US-based devices such as an iPhone access the European GPS system. Known as Galileo, the European Global Navigation Satellite System (GNSS) was brought online in 2016. At the time, it was primarily a back up plan in case the United States switched off access to GPS in a time of war or crisis.
The US-based Global Positioning System is run by the United States Air Force.
Having a secondary positioning system is also good as a backup solution in case of issues or failures of the first. From a consumer perspective, having two networks which your iPhone could access, provides faster and more accurate location information. The more satellites your iPhone can see, the better the information.