Supreme Court makes new decision after Donald Trump reintroduced 227-year-old law last used in WW2

Donald Trump's attempts to deport more people from the US using a law first made in the 18th century have been knocked back by the Supreme Court.

Back in March, Trump deported a number of people alleged to be part of a Venezuelan criminal gang, Tren de Aragua, to El Salvador, where they have been incarcerated in the country's mega-prison CECOT.

To do this, Trump used the Alien Enemies Act of 1798, which allows the US president to detain or deport people of an 'enemy nation'.

However, it's only supposed to be used if there is 'a declared war' between the US and a country or that 'any invasion or predatory incursion shall be perpetrated, attempted, or threatened'.

Drawn up in 1798 when the US thought it might end up at war with France, the old law has only been used three times in US history: the War of 1812 (which lasted until 1815), the First World War and the Second World War.

Donald Trump wants to keep deporting people out of the US under an 18th century law which needs the US to be at war (BRENDAN SMIALOWSKI/AFP via Getty Images)

The US is not at war with Venezuela, though Trump claimed that a 'foreign terrorist organisation' was 'undertaking hostile actions' against America as justification for invoking the act.

A flight with 238 alleged gang members left in March despite a federal judge ruling against the order.

It has since become clear that at least some of those deported have not committed any of the crimes they are accused of which means they have been deported in error and are now languishing in a mega-prison where inmates are subjected to horrendous conditions.

A temporary block had been placed on the deportations and the US Supreme Court voted 7-2 to reject a request from the Trump administration to clear it away.

The block will remain in place so Trump cannot simply deport alleged gang members, as the justices wrote: "Under these circumstances, notice roughly 24 hours before removal, devoid of information about how to exercise due process rights to contest that removal, surely does not pass muster."

The US Supreme Court has upheld a block on deportations, angering Trump (Matt McClain/The Washington Post via Getty Images)

Trump's failure to remove the block on deportations made him very unhappy as he wrote on Truth Social: "THE SUPREME COURT WON’T ALLOW US TO GET CRIMINALS OUT OF OUR COUNTRY!"

The US president claimed that the Supreme Court was 'not allowing me to do what I was elected to do', and he went on to claim that the court had meant 'the worst murderers, drug dealers, gang members, and even those who are mentally insane' could not be 'forced out'.

Trump argued that the Supreme Court's decision meant he couldn't deport people 'without going through a long, protracted, and expensive Legal Process, one that will take, possibly, many years for each person'.