U can't. There are so many thing, we thought to be true, modern historians found to be false. Most is to do with, corrupt authority distorting history to secure their power. This is especially the case with pre age of enlightment Europe. Other time, it is due to, as time past, certain fact got lost or history book lack certain detail and as a result, we get a distorted view of history.
Example of false history include (1) The Roman persecuting Christian, is now widely accept by historians as false history written by Catholic church, instead there was Christian version of ISIS during Roman era and those are the Christians been executed. It really was Christian terrorist who set Rome on fire rather then Emperor Nero, in fact Emperor Nero throughout his career as Emperor, order no execution of Christian that didn't break the law. (2) Muslim massacuring Christian is a lie the Catholic church create to try get Europeans to go to war with the Middle East claiming this is a Christian vs Muslim war. (3) Jesus is mythology, the truth of Jesus puzzle much historian, increase evidence today prove, Jesus never existed, instead it is originally a play inspire by Roman Emperor Tiberius that live during Jesus' time, the story of Tiberius'visit of Israel parallel the story of Jesus' preaching in Israel. It is believe the play was written to create a Jewish savior that is pro Rome, due to the Jewish myth a man name Jesus would lead them to victory. About 500 years after the play, the story of Jesus be of virgin birth, got 12 students, betray by one student, got nail to the cross and rise after 3 days was added, was been added by the Catholic church, this story parallel the story of Horris the sun god, who is of virgin birth, got 12 students betray by one and got executed but raise from the dead after 3 days.
Also 19th century Europe isn't as powerful as we today is led to believe due to a limit understanding of general public eg (1) When British defeat China in the 19th century Opium war, the British never engaged the Chinese army, because then Chinese army was on strike, the British only fought local police force (2) In the China French war, the French was defeated, but later, Cixi who hold the Emperor as a puppet, decide to end the war after 1 years, due to the newly formed army is loyal to the Emperor and Cixi fear afterwards, it would be a threat to her power (3) The only reason Britain was able to conquer India, was because India, was in civil war, afterwards, it was carved by hundred of warlords, the British East India company, was able to convince some war lords to give power to the company and ally with some warlords against other warlords that are way more powerful then the British. (e.g. Tipu sultan wiped out over 50000 British troops with only 2000 troops, later British ally with other warlords, to finally defeat Tipu Sultan) (4) Fire army such as pistol, cannons, granades, early rocket and rocket launchers are invented by Asians and passed to the west, in 13th century, due to the Mongol Empire, base on such principle by 15th century the Arabs invented the first torpedo.