Akira Amari
Akira Amari, Japan's economics minister, told reporters the countries have signed the dealReuters

The 12 countries involved with the Trans-Pacific Partnership (TPP) have signed the historic trade deal, Japanese economy minister Akira Amari has told reporters on 5 October. The deal has been years in the making, but there remains staunch opposition to the agreement, not least of all from the US political spectrum.

The deal has been one of Barack Obama's priorities in his final years as US president, and the agreement has played a significant role in the run up to the 2016 presidential elections. The Democrat is still facing a Republican majority in Congress, where even the support from his own party is weak. Debates in Congress about the TTP are expected to continue for months, and the pact will not be raised to congressmen and women until early 2016.

Republican front-runner Donald Trump and Democratic presidential hopeful Bernie Sanders have both condemned the pact. Sanders said it is a "disastrous trade agreement designed to protect the interests of the largest multi-national corporations at the expense of workers, consumers, the environment and the foundations of American democracy," and has urged voters to sign a petition against it.

The agreement, aimed at boosting trade between the partners and countering China's strong economy, means that most goods and services will be traded duty-free between the countries, and other products can be exported and imported at reduced tariffs. Signatories include Brunei, Chile, Singapore, New Zealand, United States, Australia, Peru, Vietnam, Malaysia, Mexico, Canada, and Japan.

The deal has proved contentious across a number of industries. For example, although it offers agricultural export opportunities in Japan and Canada, US milk farmers have protested the deal because it means milk from New Zealand and other countries can be cheaply imported to the US, increasing competition.