1 - Its hard to state if "labor violence" was inevitable and unavoidable, specially when not defined which side started the violence.
But two things are clear: the unions side lost many more lives than the corporates side, and in this beggining of industrialisation period there were inumerous abuses from the corporations, envolving wages, labor shifts, women and children rights. And that a study from 1969 shows that US has the the bloodiest and most violent labor history of any industrial nation in the world.
2 - The various national unions had mutual and different demands, regarding their own areas of work. Industrial workers would have different needs than construction workers, the same for rural workers and so on. But their demands were mostly envolving hour limits, child labor, workplace conditions, living wages and migrant workers.
In order to achieve their goals, unions had many tactics, some of them nowadays would be seen as guerilla tactics. Strikes were the most usual, when all workers would stop simultaneously, focusing their time in protests for their demands, usually in front of the workplace. Strikebreakers could also suffer violence from their striking peers.
Sabotage, riots and even assassination attempts were some more violent means to achieve their goals, despite the bad repercussion and legal implications.
3 - The corporations knew they needed their employees to deliver their services or products, but they know that too many labour rights would implicate in diminishing their profits. In a world coming back from the great depression, they needed to increase their gains, in orders to keep the Stock Market high. Also, in this meantime, the wolrd passed through two major conflits (WW I and II) and this also envolved the governments interest in keeping workers under control, in order to keep production of war equipments.