Most nations have periods of their history characterised by bloodshed but Russia/the Soviet Union has a good claim for the bloodiest history, especially after its experiences in the twentieth century which saw enforced death on an unprecedented scale in the Soviet Union. The Russian Empire had been no stranger to bloodshed through its history, being involved in its share of major European wars and civil unrest. But in the twentieth century it lost around two million lives in World War One and more than 10 million lives in World War Two - the most of any nation involved in these wars. Most of these deaths occurred on Soviet soil. The Russian Civil War between 1917 and 1922 claimed millions of lives and included wholesale massacres on both sides. In addition, millions died in the Soviet Union as a result of the Stalin-enforced collective farming that led to famine, or perished in Stalin's labour camps - less obviously bloody deaths maybe, but deaths none-the-less.
A lot of countries have sad histories filled with bloodshed. Rwanda,japan, US, Germany...too many countries leap to mind.
England would be in the running. They went to great lengths to achieve their empire, regardless of how many they killed.