It's a known fact that every dominating nation of its time has a very clear and well defined foreign policy. Same was the case of the Muslim Ummah for centuries under the Khilafah system.
However, today, the Ummah is in decline, and has lost its connection from Islam in societal matters, be it economics or foreign policy.
So what is Islam's foreign policy? How does it maintain relations with states beyond its frontiers? What is the reality of dawah, treaties and warfare in Islam? How would the upcoming Khilafah State deal with today's issues?