Over the past 100 years, we’ve witnessed some of the most profound changes in human history.

Between a pandemic, wars, technological developments, progress in civil rights, and breakthroughs in science and medicine, the old order has been swept away, sometimes giving way to freer forms of governing and sometimes not.

Centuries-old empires crumbled as new ideologies — from communism to fascism — took root in many parts of the world. Wars in the early part of the 20th century led to the end of the colonial world and gave birth to new nations. These wars also cost millions of lives and trillions of dollars. These are the most expensive wars in U.S. history.

Throughout the past century, technological innovations transformed our lives in ways we never dreamed. Progressive ideas also emerged and changed the world as women, African Americans, and the LGBTQ community demanded, and often won, equal rights — from the ratification of the 19th Amendment in the United States to the legalization of same-sex marriage in many countries around the world. Even so, recent civil rights protests tell us the fight for equality is not over.

The COVID-19 pandemic that is ravaging the world in 2020 reminds us that for all of our scientific breakthroughs, we’re still vulnerable to deadly viruses that can shut down economies and disrupt society. People are hoping science can save Earth from the devastating changes to the climate that continue to imperil the ecosystems of our planet. In the coming years, natural disasters may have an increasingly impactful role on the course of history. Here are 26 disaster scenarios caused by climate change.

To determine the most important event the year you were born, 24/7 Tempo drew on research materials and media sources to compile its list. Deciding the most important event in a given year is by its nature a subjective exercise. In reaching our decisions, we chose the event that had the most far-reaching impact, even if it was not necessarily the most famous event in a given year.

Click here for the most important event every year since 1920