The answer is Erosion, which is the the gradual destruction or diminution of something -- in this case, rocks. I hope this helps! For reference/perspective, sand is the product of rock erosion, because it's really just tiny remnants of crushed rock. Those "small pebbles" could be sand, but you'd have to emphasize just how small they are -- one grain of sand is just that: a grain
The liberals did not want an elected parliament.
The cause of the U.S. participation was pirates from the Barbary States seizing American merchant ships and holding the crews for ransom, demanding the U.S. pay tribute to the Barbary rulers. United States President Thomas Jefferson refused to pay this tribute. Sweden had been at war with the Tripolitans since 1800.
During the century that followed Pax Romana, Rome had many leaders because men were fighting for power of the empire. This time period is know as "The Crisis of the Third Century ". It was during this time that the Roman Empire almost collapsed entirely because of several combined pressures including civil war, invasions, plague and economic depression.
