Treaties are a key part of the trust between countries. Treaties go hundred of years. They worked then and they still work today. There is no reason as to why we need to break into all out war over a confrontation when we can simply agree to a peaceful treaty that will benefit both sides.
Treaties are most definitely still needed in today's society. Without them, there are no rules or regulation for countries that interact with each other to go on. Chaos would ensue if we did not have treaties. Provinces and countries would just act in ways that had no regard for anyone but themselves, which could have devastating effects.
Without treaties, nations, countries, and provinces will not have a guideline to ground them when they deal with each other. It is important that different states and countries be diplomatic with each other. Diplomacy is what allows peace to take place and treaties are one of the main tools of diplomacy. As long as humans have emotions, war is a possibility and it is important that all forms of diplomacy are practiced in order to avoid war when a difference of opinion or belief exist between two countries or nations.
No, treaties are not necessary now. We are living in the 21st century where there are multiple truths. Besides, the context in which the treaties were made is not or cannot be the context now. It is necessary to provide a room for dynamism. What was cannot be what is now.