All throughout Psalms and various parts of the Bible, the term "nations" is mentioned. Groups of people, individuals, countries...they all can be defined as nations. In the Bible, there are many many different cultures, languages, and races that help us understand "nations" better. Since they are all different, most of them actually are not aware of Jesus Christ and what He did for us. We are called, as believers of Christ, to make disciples of ALL NATIONS. This means Christ tells all of us to spread the Gospel to all parts of the world. Our own community, different groups, cultures, races, religions etc. Us (as Christians) are called to go after each nation or people group that hasn't heard of Christ. Psalms 67:2 says "that your ways may be known on earth , your salvation among all nations." This is a psalm written proclaiming to God that His word will be carried out to all people through us (His disciples). It's up to us to live our lives to the fullest, spreading His love to every single person/nation that we encounter.
There are different types of nations. A nation where Christ is well-known and a nation where the people are unreached/unengaged in Christianity. A majority of nations in the eastern world, practice religions outside of Christ. We live in a culture, that is the direct opposite. We live in fellowship with one another and where Christ is constantly surrounding us and impacting our lives and the lives directly surrounding us. However, if we take ourselves out of the bubble we have created, surrounding ourselves with nations that have never heard about Jesus Christ, we are then doing what God called us to do. Making disciples of ALL nations.