A theorem of van Dantzig from the 1930s, stating that every such group contains a compact open subgroup, was all that was known. Then groundbreaking work by George Willis  in 1994, opened up the field by showing that every locally compact totally disconnected group contains a so-called tidy subgroup and a special function on its automorphisms, the scale function, giving a quantifiable parameter for the local structure.
A theorem of van Dantzig from the 1930s, asserting that every such group includes a compact open subgroup, was all that was known. Then pioneering work by George Willis in 1994, expanded the field by revealing that every locally compact totally disconnected group contains a tidy subgroup and a special function on its automorphisms, called the scale function, providing a measurable parameter for local structure.