Responsive page with API, built with Flexbox, Grid and theme toggler

I have successfully finished this project but I struggled with React a little bit, especially with the idea I had. So, one of the functionalities required says that users should be able to click through to the border countries on the detail page. I tried to manage that with React Router, but didn't quite know how to do that, so in the end I used conditional rendering to navigate between home and detail pages, and didn't use border countries as links to their detail pages. How would you solve this problem?