If all Schleswig joined Denmark after World War I

How would Germany and the invasion of Denmark change if all Schleswig had voted to join Denmark after World War I?

The loss would strengthen German revisionist rhetoric but also give Denmark more depth and the Kiel Canal as a defensible boundary, likely extending resistance rather than preventing invasion.

Schleswig could become another territorial grievance in Hitler's rhetoric, giving Denmark more warning as well as more territory and population to defend. A frontier near the Kiel Canal would force German forces to begin farther south in Holstein and cross bridges and narrow approaches. Artillery covering those crossings could delay movement and complicate supply. An initial estimate of 12-18 hours of resistance remains speculative, and the discussion also considers longer delays at particular crossings alongside the threat of bombing. Extra warning and depth could allow Danish warships to escape, while German airborne troops committed there would be unavailable for Norway. The counterfactual changes the timing and complexity of the invasion without establishing that Denmark could defeat it.