The invention of the internal combustion engine opens the way to modern day transport as we know it. Although the steam engine had already started a revolution in transport, and the smoke-belching iron monsters were crossing Europe on their rails, common people couldn't make such a good use of it. After all, it proved really difficult to make the steam engine small enough for personal transport; and here's where combustion comes in - it smethod of transforming energy into motion could be fit into a machine the size of a carriage.