Factors responsible for environmental improvements in eastern europe during the 1990s included:

car ownership trends
eu membership
industrial closures
international investment
privatization
the end of collectives
the end of the soviet union

president thomas jefferson commissioned the expedition shortly after the louisiana purchase in 1803 to explore and to map the newly acquired territory, to find a practical route across the western half of the continent, and to establish an american presence in this territory before britain and other european powers