Final answer:
The Frank family had to hide in the annex during World War II because they were being persecuted by the Nazis. They were able to hide for two years with the help of Dutch friends, but were eventually discovered and sent to concentration camps. Anne Frank's diary provides an important record of their time in hiding.
Step-by-step explanation:
The Frank family had to hide in the annex during World War II because they were being persecuted by the Nazi society. In 1940, the Germans occupied the Netherlands and began sending Dutch Jews to extermination camps. To avoid being captured, the Frank family went into hiding in a secret annex with others, supported by a network of Dutch friends in the underground resistance.
They remained hidden for two years, but were eventually discovered by German authorities in August 1944 and sent to concentration camps. Anne Frank, the youngest member of the family, had kept a diary during their time in hiding, which was published after the war and became an important record of the Holocaust.
Despite efforts to deny the Holocaust, there is irrefutable evidence that it took place and millions of lives were lost.