How did my hub appear on the first page on Google search one day after publishing?

Hilly is right ... On an exact phrase search I found 26 pages in competition for this phrase, all for an ad cost of a nickel (*sigh*), and the strength of the competition for this phrase is zero, so you might see this one climb to the top of the Google ranking within a month or two.

Unfortunately, it received less than 30 searches last month. :(

I wrote an excellent hub on keyword research that will help those interested discover better keywords. You'll find it here:

http://hubpages.com/hub/Yoshis-Hubbing-101-Finding

While you can no longer change the URL, which would garner much more hits, you could change the title to something like ... 'My immigration to America', which would help, as the phrase 'Immigration to America' gets about 880 hits a month, pays a percentage of 1.04 per ad clicked, and has a relatively low strength of competition and 77,000 pages in competition.

Now, 77,000 seems like a lot, but through some good backlinking you could bump yourself slowly up the ladder over several months. :)

I'm going to write another hub on the importance of the keyword that should help, so be on the lookout for it.. :)

It's because it's not a common phrase, not many people have the words used in that order on their websites and no-one has it in their url like you do. Unfortunately not many people will be searching for that phrase either, if people find your hub it will almost certain that it will be for other phases that you use in your hub.