Talking about being in or going to a country, city, or region uses a specific set of prepositions rather than one all-purpose word like English "in/to". Cities normally take à: à Paris, à Londres. Feminine countries (most countries ending in -e) take en: en France, en Espagne, en Chine.
Masculine countries take au: au Japon, au Canada, au Brésil — and plural-named countries take aux: aux États-Unis, aux Pays-Bas. This pattern extends the au/aux contractions already seen with à + le/les, since most masculine and plural country names are grammatically treated as if introduced by le or les.