Mountains, highlands and rivers.
The Articles of confederation was weak in that it had no power to tax, it couldnot enforce the laws in the constitution and couldn't maintain an army.In this case, the central government couldn't accoplish anything because it had no authority as all powers were placed on the states.
The Shays rebellion demostrated to the governement the need for a strong central government, one that could stand firm on basis of its laws and the constitution.This was achieved through the first revolution under the new government that led to the formation of a central government with strong powers and control.
In addition to that, the articles of confederation was weak because it prohibited the collection of direct taxes on income and property yet these taxes were necessary to facilitate the payment of war debts and to enable the country have a working economy.Shays rebellion exposed these weaknessess fro correction.
Ferdinand Magellan was the first (at least his crew) to successfully lead an expedition to circumnavigate the world. (he died on the voyage, but ~3 sailors made it back i believe, forgot the number of sailors, but very little)
hope this helps
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