Google Calendar shows only some events, or nothing at all.

Go to the My calendars page. Click Edit on the calendar which you want to extend.

Open the Time period tab and adjust the time periods to your liking. Try one month or at most six months.

The Time period tab is not shown on phones due to their small screen size. You'll need to adjust this setting with a tablet or a computer. The extended calendar, however, will work fine with phones as well.

Finally, click Save.

Your calendar is now small enough, but Google does not know about it. You can either wait for Google to download the updated calendar, or do it manually.

If you want to do it manually and see the results quicker, please take a look at How do I force my calendar application to refresh a calendar subscription?