Italy's unification, which was completed in 1870, was accomplished by the leadership of Camilo Cavour and Giuseppe Garibaldi. It was done with the help of foreign powers. Therefore, Italy became unified though Italian leadership and foreign help.
Cavour got the last push for Italian unification started in 1858 when he made a deal with France. Cavour's state, Piedmont in Northern Italy, would give France some of its territory in what is now France in return for French help in driving out the Austrians, who were in control of most of Italy. France did not completely fulfill its part of the bargain, but Italy was on its way to being unified.
In 1860, Garibaldi raised a volunteer army and began fighting for Italian unity. He conquered much of Southern Italy. At that point, Cavour's armies linked up with his and claimed most of what is now Italy, creating the country of Italy in 1861.
The unification was completed in 1870, this time with Prussian help. Prussia and Italy allied together in wars in 1866 and 1870, defeating Austria and France respectively. These wars ejected the Austrians and French from Italy and Italy was able to be completely united in 1870.