A trade union is exactly what its name suggests - it is a union of people for the sake of their trade. In other words, it is an organization of workers in order to achieve certain common goals like increment of wages, better working conditions, etc.
The history of labor union dates back to the guild system that started in Europe, this system aimed to protect selected professions by controlling of advancement and skill mastery. This is how unions came into existence, and is the first example of how numerous workers join together to create their own rules instead of following those set by their employers.
A great demand for new workers to join the job market was triggered by the eighteenth century's industrial revolution in Europe. In the US in earlier times the trade unions and workers played a very important part in striving for their independence. They introduced physical efforts as well as ideas and although the former were not useful or successful, the latter remained in the American Culture and are still followed to this day.
It was only in the nineteenth century that the union became hugely popular after the founding of the National Labor Union, which is the very first national union. This union was formed in the year 1866 and it was open for all kinds of workers. Unfortunately, this union wasn't successful and was dissolved shortly and all that remains in the history is its foundation. Later on in the year 1869, the Knights of Labor was created and it was this union opposed child labor and promoted the idea of working for eight hours a day. It was so successful that the membership zoomed up to a staggering 700,000 members!
And that is how trade unions came into existence. It all started as a great idea and became what we see it today. Although the agendas of today's union might have changed, but the ideals and aims more or less remains the same.Origin and History of Trade Unions