There are 195 countries in the world today according to the United Nations. This total comprises 193 countries that are member states of the United Nations. Plus 2 countries are non-member observer states: the Holy See (Vatican City) and the State of Palestine.
Of course, there are disputed territories (such as Kosovo, Taiwan and Western Sahara). And dependent territories (Cook Islands, Puerto Rico and Aruba). And territories with special status (Hong Kong and Macau). But initially, we were aiming to stick to the UN list.
We have decided to visit all 10 disputed territories as well, but that might take a few more years. So now, the aim is to visit all 195 countries by 2022 + 10 disputed territories by 2030.