Why are modern governments larger than in the past (19th century or earlier)? Why was the army the largest part of the budget?

My guess is that such societies were de facto ruled by an oligarchy of military, nobility or businessmen which managed the government for their own interest and were willing to let the bulk of the population live in poverty, along with that, in the 19th century war was far more common and the army was more necessary. With the passage of time, governance came under the influence of the will of the population, increasing welfare expenditure and after the world wars, warfare became less relevant.