What are the most significant tragic events that have been covered up in the history of mankind?

 It's important to note that discussions about covered-up or suppressed historical events often involve controversies, conspiracy theories, and varying perspectives. While some events may be subject to disputes, it is crucial to rely on well-documented evidence and scholarly research when considering historical narratives. That being said, there are instances where significant events faced suppression, denial, or limited acknowledgment. Here are a few examples:

1. **Holocaust Denial:** Despite overwhelming evidence and historical documentation, there have been individuals and groups who have denied or minimized the extent of the Holocaust, during which millions of Jews and others were systematically murdered by the Nazis during World War II.

2. **Armenian Genocide:** The mass killings and deportations of Armenians by the Ottoman Empire during World War I are a contentious historical issue. While many scholars and countries recognize it as a genocide, the Turkish government has historically denied this characterization.

3. **Tiananmen Square Protests (1989):** The Chinese government has downplayed and suppressed information about the violent crackdown on pro-democracy demonstrators in Tiananmen Square in Beijing. The exact number of casualties and the events leading up to the crackdown remain sensitive topics in China.

4. **Stalin's Purges and Famine:** The extent of Joseph Stalin's purges and the man-made famine known as the Holodomor in the Soviet Union during the 1930s were downplayed or denied by the Soviet government for many years. The true scale of these tragedies became more widely acknowledged after the dissolution of the Soviet Union.

5. **Unit 731 Experiments:** During World War II, Japan's Unit 731 conducted human experimentation, including biological and chemical warfare experiments, on prisoners of war. The details of these war crimes were hidden for many years, and it wasn't until later that the information became more widely known.

6. **Operation Condor:** A covert campaign of political repression and state-sponsored terrorism conducted by several South American dictatorships in the 1970s and 1980s. The full extent of the operation and the atrocities committed were not fully acknowledged until years later.

It's important to approach discussions about historical events with a critical mindset, considering credible sources and multiple perspectives. While some events have been suppressed or denied, historical scholarship and investigative journalism play a crucial role in uncovering and documenting the truth over time.