In Islam, two condition must be met before war is permitted:
- lack of treaty
- breach of treaty
If there is no treaty between two nations, then war against that nation (group of people) is an acceptable policy in Islam, but if the opposition seeks to negotiate a treaty, then negotiation is advised.
If there is a treaty already in place, and the other nation breaches its regulations, then once again, war against that nation (group of people) is acceptable, but if the other nation decides to negotiate a new treaty, then negotiation is advise.
Peaceful interaction between an Islamic State and an unIslamic State is through a treaty.
The above information is extracted from Quran and Ahadith in their context.