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 from van Dantzig's 1930s indicating the presence of a compact open subgroup in every such group was previously understood. Subsequently, George Willis's work in 1994 broadened our knowledge by showing that every locally compact totally disconnected group includes a tidy subgroup and a special function on its automorphisms, known as the scale function, which provides a measure for local structure.