Agreed that "nature" is a pretty big term but one thing you might want to look at is the "cult of the offensive" which may explain both why wwi started and why it was so bloody. Stephen van evera has a great article on it.

Basically a number of social and political factors led leaders to believe in a significant offensive advantage. This was also fuelled in part to misperceptions about the uses of new firearms like machine guns. Leaders thought that the increase in firepower magnified the attackers advantage. Leaders also tended to discount the defensive advantages of barbed wire and railroads.

Because there was an advantage to attacking, countries became much more aggressive as attacking was both a means of gaining power and insuring against the loss of power. This fuelled brinksmanship and arms races, as well as poor tactics during wwi.

Can you clarify what you mean about "the nature" of it? Because I'm tossing around like 3 different ways I can interpret that and they'd get pretty separate answers.