how did britain became a friendly country which was the arch anemy during the war?

Friendly to whom and after which war?

If you mean Britain was the archenemy of the USA and France. Then lets check the two country out.(A quick breakdown)

USA fought two wars with Britain but due to WWI, Britain became allies with the USA for support and troops and the WWII as the Axis/Japan bomb Pearl Harbor.

France and Britain became allies over the Crimean War to prevent the Russians from invading Turkey. Then fought together in WWI and WWII plus in the Sue Canal.

Really, friendly to whom and what timeline? and after what event? Just like Damon said!

Britain and its relationship with other countries, including those it was once enemies with, have evolved over time. In the context of your question, it seems you are referring to how Britain and Germany, particularly during World War II, transformed their relationship from being arch-enemies to becoming friendly countries.

To understand this transformation, it's important to consider the factors that led to the change in their relationship. Here are some key points:

1. Post-war Reconstruction and European Integration: After World War II, Europe was devastated, and there was a strong desire to prevent future conflicts. The idea of European integration emerged, leading to the establishment of organizations like the European Coal and Steel Community (ECSC) and later the European Union (EU). These efforts aimed to foster peace, cooperation, and mutual prosperity among European nations, including Britain and Germany.

2. Reconciliation and Tackling the Past: Post-war leaders in both Britain and Germany recognized the need for reconciliation and addressing the atrocities committed during the war. They encouraged dialogue, acknowledgment of mistakes, and understanding between their nations. Leaders from both countries engaged in efforts to promote reconciliation and build bridges between their societies.

3. Economic Cooperation: Economic ties and mutual interests played a significant role in fostering friendship between Britain and Germany. Both nations recognized the benefits of economic cooperation, trade, and investment. Over time, they developed strong economic relationships, which facilitated trust and cooperation.

4. Cultural and Educational Exchanges: People-to-people exchanges through cultural and educational initiatives also contributed to the transformation of relations between Britain and Germany. Encouraging cross-cultural understanding, promoting language learning, and facilitating educational exchanges helped bridge the gap between the two nations and build positive relationships at the individual level.

It is essential to note that while Britain and Germany have become friendly countries and partners in various international and economic endeavors, the process of reconciliation and overcoming historical animosities took time and involved the efforts of leaders, diplomats, and citizens from both countries.

By acknowledging their shared history, engaging in dialogue, fostering mutual interests, and promoting understanding, Britain and Germany were able to transform their relationship from being arch-enemies to becoming friendly nations.