1444 --- The Beginning of the Portuguese Slave Trade

1128 -- Founding of Portugal

Portugal traces its national origin to 24 June 1128, the date of the Battle of São Mamede. Afonso proclaimed himself Prince of Portugal after this battle and in 1139, he assumed the title King of Portugal. 

1255 -- Lisbon becomes capital of Portugal
1346 -- Portugal claims the Canary Islands

1385 -- John I (House of Aviz) wins undisputed kingship in Portugal with help of English archers.

1386 -- Portugal and England make alliance in the the Treaty of Windsor, which exists to the present day.

sealed by the marriage of King John I of Portugal to Philippa of Lancaster, daughter of John of Gaunt, 1st Duke of Lancaster.

It is the oldest alliance based on known history in the world that is still in force by politics

1394 -- Birth of Prince Henry the Navigator

Henry was the third surviving son of King John I of Portugal and his wife Philippa, sister of King Henry IV of England.

1415 -- Portugal conquers Ceuta, a city on the Africa coast of the Strait of Gibraltar. Prince Henry learns about the wonders of the Saharan trade.

Henry encouraged his father to conquer Ceuta (1415), the Muslim port on the North African coast across the Straits of Gibraltar from the Iberian Peninsula. He learned of the opportunities offered by the Saharan trade routes that terminated there, and became fascinated with Africa in general; he was most intrigued by the Christian legend of Prester John and the expansion of Portuguese trade. He is regarded as the patron of Portuguese exploration.

1418 -- Portuguese encounter the Madeira Islands.

1419 -- Prince Henry's father appoints him governor of the Algarve (southern Portugal).

1420 -- Prince Henry obtains appointment as the Grand Master of the Military Order of Christ, the Portuguese successor to the Knights Templar, which had its headquarters at Tomar, in central Portugal.

1425 -- Henry's brother makes a trip of Europe, returns from Venice with a current world map
1427 -- Portuguese encounter the Azores.

1434 --  Gil Eanes, the commander of one of Henry's expeditions, becomes the first European known to pass Cape Bojador (Western Sahara).

Until Henry's time, Cape Bojador remained the most southerly point known to Europeans on the desert coast of Africa. Superstitious seafarers held that beyond the cape lay sea monsters and the edge of the world.

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1437 -- Henry organizes disastrous Portuguese expedition to Tangiers

1441 -- Portuguese round Cape Blanco (border between modern Western Sahara and Mauritania)
1443 -- Portuguese sight  Bay of Arguin on the coast of Mauritania.

1444 -- Portuguese encounter the Senegal River and round the peninsula of Cap-Vert. Beginning of the Portuguese slave trade.

By this stage the explorers had passed the southern boundary of the desert, and from then on Henry had one of his wishes fulfilled: the Portuguese had circumvented the Muslim land-based trade routes across the western Sahara Desert, and slaves and gold began arriving in Portugal.

1448 -- Portuguese build fort at Bay of Arguin (Mauritania).