Portugal introduced the tempura-style frying method to Japan in the 16th century.
Portuguese traders and Jesuit missionaries reached Japan during the Nanban trade period, bringing European techniques for coating food in flour-based batter and frying it. One related Portuguese dish was peixinhos da horta, usually battered and fried green beans. The method was adapted in Nagasaki and eventually became associated with seafood and vegetables.
The word “tempura” is often linked to Latin tempora, referring to Catholic fasting periods when missionaries avoided meat and ate fried vegetables or seafood instead. The exact etymology is discussed, but the Portuguese connection is the standard account in descriptions of tempura’s history.
Modern Japanese tempura is not simply unchanged Portuguese food. Japanese cooks refined the batter, frying technique, ingredients, and serving style. In the Edo period, tempura became a popular street food, typically served with a dipping sauce. Spain and the Netherlands also had contact with Japan, but Portugal is the canonical answer for this culinary influence.