The Treaty of Windsor was signed in 1386 between the Kingdom of England and the Kingdom of Portugal. This agreement established a strong alliance, promoting mutual support in military and trade matters. It is one of the oldest diplomatic treaties still in effect today, highlighting the enduring relationship between the two nations. The treaty was significant for both countries, as it allowed Portugal to gain military assistance from England against its enemies, while England benefited from access to Portuguese resources and trade routes. This alliance laid the groundwork for future cooperation and strengthened ties between the two countries over the centuries.