What changed between President Tyler's initial attempt to annex Texas in 1844 and his successful effort in early 1845 can be attributed to a combination of political developments and changing circumstances:
Presidential Election of 1844: In 1844, President Tyler's push for the annexation of Texas became a contentious issue in the presidential election. The Democratic Party was divided on the question of annexation, with some members favoring it and others opposing. Tyler, who had ascended to the presidency after the death of President William Henry Harrison, was not seen as a strong candidate for re-election.
Change in Leadership: After the 1844 election, James K. Polk, a strong advocate for the annexation of Texas, was elected as the President of the United States. His victory reflected the public's support for annexation, and it allowed for a more cohesive approach to the issue.
Compromise with the British: The U.S. and the British had been in negotiations regarding the border between Oregon (which included the present-day states of Oregon and Washington) and British-held territories. A compromise was reached in the form of the Oregon Treaty in June 1846. This reduced tensions with Britain and allowed the U.S. to focus more on annexing Texas without the distraction of a potential conflict.
Joint Resolution of Congress: In early 1845, shortly before James K. Polk took office, President Tyler was able to get both Houses of Congress to pass a joint resolution for the annexation of Texas. This approach, rather than a treaty, required a simple majority vote in Congress and was seen as a more achievable path for annexation.
Strong Advocacy: President Polk was a vocal supporter of annexation, and his administration made it a top priority. This strong advocacy helped secure the necessary support in Congress.
In summary, the change in presidential leadership, the public's support for annexation, the resolution of issues with Britain, and a strategic shift to a joint resolution in Congress were key factors that allowed for the successful annexation of Texas in early 1845, following President Tyler's initial failed attempt in 1844.