Donald Trump vowed to be tough on crime and illegal immigrants in a speech accepting the Republican presidential nomination.
Mr Trump's 75-minute speech was designed to set the tone for the general election campaign against Hillary Clinton, an answer to Republicans who say the best way he can unify the divided party is to detail why she should not be elected on 8 November.
He accused her of a legacy of "death, destruction, terrorism and weakness" as US secretary of state.
As the crowd chanted: "Lock her up" for her handling of US foreign policy, Mr Trump waved them off and said: "Let's defeat her in November."
Thousands of supporters who were gathered in the convention hall roared their approval.
When it was over, Mr Trump was joined on stage by family members as balloons cascaded from above and confetti blew around the arena.
A CNN snap poll of viewers of the speech said 57% had a "very positive reaction" to the address and 18% a somewhat positive reaction, while 24% said it had a negative effect.
Social media sentiment toward Mr Trump based on tweets that mentioned his name was slightly more negative than positive shortly after his speech.
The acceptance speech by Mr Trump closed out a four-day convention that underscored his struggle to heal unease in the Republican Party over his anti-illegal-immigrant rhetoric and concerns about his temperament.
The event was boycotted by many big-name establishment Republicans, such as 2012 nominee Mitt Romney and members of the Bush family that gave the party its last two presidents.
Mr Trump presented a bleak view of America under siege from illegal immigrants, threatened by so-called Islamic State militants, hindered by crumbling infrastructure and weakened by unfair trade deals and race-related violence.
Accusing illegal immigrants of taking jobs from US citizens and committing crimes, Mr Trump vowed to build a "great border wall" against the border-crossers.
He took positions in conflict with traditional Republican policies.
He said he would avoid multinational trade deals but instead pursue agreements with individual countries.
He would renegotiate the NAFTA trade accord linking the United States, Canada and Mexico. He would penalise companies that outsource jobs and then export their foreign-made products back into the United States.
"We will never sign bad trade deals," Mr Trump said."America first!"
The New York businessman, who has never held elected office, filled his speech with some of the bravado he used to win the Republican nomination over 16 rivals.
"I have joined the political arena so that the powerful can no longer beat up on people that cannot defend themselves," Mr Trump said. "Nobody knows the system better than me, which is why I alone can fix it."
In his speech, he portrayed himself as a fresh alternative to traditional politicians, willing to consider new approaches to vexing problems and help working-class people who may feel abandoned.
Laying out his case against Mrs Clinton, he denounced nation-building policies that were actually put in place to some extent by George W Bush, without mentioning by name the Republican president who launched wars in Afghanistan and Iraq.
Mr Trump said policies pursued by Mrs Clinton in Iraq, Libya, Egypt and Syria had made a bad situation worse. He blamed her for the rise of so-called Islamic State militants and blasted her willingness to accept thousands of Syrian refugees.
"After 15 years of wars in the Middle East, after trillions of dollars spent and thousands of lives lost, the situation is worse than it has ever been before. This is the legacy of Hillary Clinton: death, destruction, terrorism and weakness," Mr Trump said.
Clinton senior adviser John Podesta dismissed the speech as painting "a dark picture of an America in decline" and called it a reminder that Mr Trump "is temperamentally unfit and totally unqualified to be president of the United States."
John Weaver, a senior adviser to Ohio Republican Governor John Kasich, a former presidential rival to Mr Trump, said in a tweet that Mr Trump had delivered the "saddest, darkest, most depressing acceptance speech in modern history."
Mrs Clinton fired off a icy rebuke, telling Mr Trump: "We are better than this."
Her one-line tweet came midway through his acceptance speech.
We are better than this.
— Hillary Clinton (@HillaryClinton) July 22, 2016
The text of Mr Trump's speech, released by his campaign, included extensive footnotes to show where the material originated.
That was perhaps in reaction to the speech given on Monday night by his wife Melania, who was accused of plagiarism when she repeated lines from a 2008 speech by Michelle Obama.
Five talking points from Donald Trump's GOP acceptance speech at the Republican National Convention.https://t.co/l21ya4JfVp
— RTÉ News (@rtenews) July 22, 2016
