In previous times, the diplomatic relations among states usually comprises negotiation, arbitration, mediation and treaties. So, Osmanli did having some treaties and negotiations with other states, including the European states.
Gift exchanges often being practiced during that time. For example during the time of Sultan Suleyman, he received an expensive portrait of Mehemmed al-Fatih made by a famous Italian artist. Usually, this gifts exchange symbolized recognition of superiority of the state. Although the Osmanli and Mamluks sometimes were not having a good relation, they indeed have a good time together. Just like when Sultan Murad 1’s time, while the Osmanlis were preparing to march to another state, then the Borquq envoy arrived, bringing together with them gold and precious gifts to be given to the Sultan. And later, Sultan Murad replied by giving a huge number of gold back to the ruler of Egypt.
Another practice is based on marriages. Some sultans, kings or noblemen married their sons or daughters to another ruler’s child to strengthen the states’ relationship. For example, Gazi Sultan Murad marrried his son, Yildrim Beyazid to the daughter of Suleyman Shah (the ruler of Germiyan Emirate). From that marriage, he received few states as dowry.
Osmanli was also having a good relationship with European states, especially in trading system. The merchants came to Osmanli territories brought benefits to the devlet. To attract more European merchants coming into Osmanli areas, the sultan established the Ahdname system.
Ahdname system is literally known as the letter of promise. This letter of promise was not a peace treaty, but basically it was a business treaty. As for that time, ambassadors usually represented the merchants and not the political leaders. This ahdname system is the high-ranking system containing oath made by the Osmanli sultan declaring the diplomatic and commercial relation between the states, the privileges, rights and personal immunities of the ambassador while being in the Osmanli areas. This means, the ambassadors were freed to Osmanli’s prosecution, judicial power and conscriptions. This led to more and more European people came into Osmanli territory.
Besides, the action of giving honorary titles to the leaders also became known as the style of diplomatic relations at that time. For example, Sultanu Guzat al-Mujahidin of Mamluks was called as Sultan of Champions and Warriors of the Faith. Another example is the title Al- Janab Al-Ali Al-Amiri, given to Mehmet 1 by the Mamluk officials. And even Sultan Mehemmed al-Fatih was given several good titles symbolizing his victory defeating Byzantine and opening Constantinople to Islam.
After the Byzantine Empire ended, the European power started to move into the Asian continent. The Portuguese at that time reached India. So, Mughal sultan at that time, Akbar asked help from Osmanli devlet to defeat the Portuguese influence in India. So, Osmanli sent such a big number of forces to India and helped Humayun against the Portuguese. This helped India free from Portuguese attacks for about two and a half centuries.
The relation between Osmanli and Safavid was also sometimes good, despite their endless wars. They did have several treaties made before waging wars again and again. Even after the victory of Sultan Mehemmed al-Fatih opening Constantinople, he even sent the letter of announcing the success to the Safavid sultan to share the great news.