Yeah you definitely need Redux or another state management solution. One of the unorthodox practices React encourages (through the Flux architecture) is to have 'global' state that components can access without passing down props all the time. Currently I limit setState usage to things that only the current component cares about, like if a button is disabled. Every event that may affect another component dispatches an update to the Redux store which holds the global state object.

Some Redux resources:

1) Getting Started with Redux, videos from its creator: https://egghead.io/series/getting-started-with-redux

2) Simplest Redux example (including ES5): https://github.com/jackielii/simplest-redux-example

3) I added Redux to the example app from the docs: https://medium.com/@firasd/quick-start-tutorial-using-redux-...

4) Offical Redux repo, including many examples https://github.com/reactjs/redux