1) Nuclear weapons
Nuclear Weapons are the most deadliest weapons in history. The introduction of nuclear weapons has provided humankind with the ability to inflict upon itself the sort of extinction level event that was impossible.The atomic bomb dropped on Hiroshima killed 70,000 people initially, with tens of thousands more exposing to radiation sickness over subsequent months and years.
2) Biological Weapons
In the history of armed war, disease has often claimed more lives than any combat. Intentionally introducing some deadly virus to the battlefield is a dubious strategy at best, however, as biological weapons tend to be even more capable than chemical weapons. Viruses and bacteria do not discriminate on any basis. Biological weapons are banned under the Geneva Protocol of 1925 but still Japan used biological weapons in China and had reportedly conducted an extensive experimentation program that killed over 3,000 human test subjects.Biological weapons has been in use since the ancient times.
3) Maxim Machine Gun
The 19th century saw a change in firearms technology which comes as a revolution in the firearms industry. The innovation was the introduction of cartridge ammunition and constant firing mechanism. Smokeless powder burned more cleanly better than black powder. Hiram Maxim was the inventor to incorporate all of these innovations into a single weapon which can fire more than 500 rounds per minute over an effective range of more than 2,000. It is included in the list because it took a huge number of lives during the World War.