Conversation so far:
What were the European pressure?
The fall of the Liberal government in 1874 meant the repeal campaign stalled. Although the LNA kept the pressure, persuading Liberal MPs to oppose the Contagious Diseases Acts was slow.
When did the pressures come?
December 1874, Butler left for France, Italy and Switzerland, where she met with local pressure groups. March 1875, Butler formed the British and Continental Federation for the Abolition of Prostitution.

Question: What was the white slave trade?
Self-contained rewrite: What was the white slave trade in the 19th century?