A tag management system is a control layer that loads analytics, advertising, consent and marketing scripts onto a website without a code change for every adjustment. Marketing and web teams use it to deploy tags, define triggers and manage consent-dependent behaviour from one interface.
From a sovereignty view, a tag manager is the gatekeeper for everything that happens in a visitor's browser. Whoever controls the container can add scripts that read or send data, and one misconfigured tag can pass identifiers to third parties outside the EU. The ePrivacy rules on accessing information on a user's device, which the EDPB has clarified in its guidelines on Article 5(3), apply to tags whether or not personal data is involved. Lock-in sits in the container configuration: triggers, variables and tags are rarely portable between tools.
When selecting a European option, check whether server-side tagging can be hosted by you, whether the script library is served from the EU, whether it integrates natively with a consent platform that blocks tags until consent is given, and whether changes and access rights are logged.