This is Part II of an article. Part I is here.
Because technology is such a key element in determining relative strength, and because the off-planet beings are visiting us, and not the other way around, it is likely that the off-planet culture which descends through our atmosphere will be more powerful than we are. Thus, we must study examples from history, with an eye toward how the less powerful group handled the meeting.
Japan was closed to outsiders from around 1603 up until 1854. Prior to the earlier date, Japan was well-disposed to foreign trade and Christian missionaries. But one of the Shoguns began to fear native Christians would set up a fifth column for Spanish or Portuguese invaders. So he expelled the foreigners and closed the borders.
While the American, Matthew Perry, was largely responsible for re-opening Japan, it was the Russians who inadvertently gave the Japanese the keys to modern technology. "While continuing negotiations with the Japanese, Putiatin (a Russian) asked permission for his men to build a vessel to take (the ship-wrecked Japanese) home. Because [a Japanese leader] had lifted the restriction against building large ships, the Russian admiral’s request was granted. The Japanese watched intently and soon afterwards built an exact copy. The bold claim that the Japanese could quickly catch up technologically with the West was realized and demonstrated to devastating effect only fifty years later in the Straits of Tsushima, where virtually every ship of the Russian fleet was sunk or captured by Admiral Togo."
Source: http://www.navyandmarine.org/ondeck/1800perryjapan.htm, Apr 28, 2011
In this example, Japan was well aware of both the advantages and risks of opening contacts with an alien culture. Where they saw a power imbalance, they always worked to strengthen themselves. Unfortunately, the friendly relationship with the West decayed into war on more than one occasion.
** End of Part II **