How to use the Main Timeline
By default the Timeline shows events for all countries in columns, side-by-side, left to right, in the order Austria-Hungary, Germany, Serbia, Russia, Britain, France, Belgium.
If your screen is set to 1280 horizontal pixels wide you see the first three country columns. You scroll right to see the others, and scroll left to comeback.
View one country at a time
To concentrate on a particular country you can remove the other countries from view by clicking on the flags of those countries. The country columns disappear. The flags go dim. Clicking on a dim county flag brings that country back. Clicking on ALL brings all countries back.
View selected countries side-by-side
By clicking on the appropriate national flags to remove countries from view you can compare different combinations of countries side-by-side.
Alternative way to study the Timeline
You can see the Main Timeline in smaller amounts by going to the TOP TIMELINE and clicking on any day in any country. This brings up the detail for only that day in that country.