String Universality and Non-Simply-Connected Gauge Groups in 8d

We present a consistency condition for 8D N=1 supergravity theories with nontrivial global structure G/Z for the non-Abelian gauge group, based on an anomaly involving the Z 1-form center symmetry. The interplay with other swampland criteria identifies the majority of 8D theories with gauge group G/Z, which have no string theory realization, as inconsistent quantum theories when coupled to gravity. While this condition is equivalent to geometric properties of elliptic K3 surfaces in F-theory compactifications, it constrains the unexplored landscape of gauge groups in other 8D string models.