In Washington, demonstrators arriving by auto, bus or subway converged on the city's Freedom Plaza and marched defiantly past the nearby Trump International Hotel on Pennsylvania Avenue.
Many wore pink "pussy" hats to protest Trump's demeaning comments about women.
"We are all part of the same movement, regardless of any divisiveness or any drama that goes on", Ms Sanchez said.
This year's march came against the backdrop of a partial government shutdown, now in its 29th day, that started after Trump refused to back down on his demand for more than $5bn in funding for a wall on the USA southern border.
Some held signs that called for Trump to be impeached, others emphasised the need to believe survivors of sexual assault and rape, and many demanded an end to the shutdown.
While the founder of the Women's March a year ago called on its controversial cochairs to step down, they declined, and instead added to the official Women's March agenda a defense of the boycott, divestment and sanctions movement of Israel.
Just blocks away, the president spoke to reporters outside the White House before traveling briefly to Dover, Delaware for a ceremony to receive the remains of four Americans killed in an attack claimed by the Islamic State group in Syria.
Far-left activist Linda Sarsour made the anti-Semitic remarks, screaming, "Anything from Medicare for all, to ending the war in Yemen, to standing up for free speech and our constitutional right to Boycott, Divestment, and Sanctions in these United States of America".
Women gathered in London at Portland Place.
In New York, several hundred people had converged on Manhattan's Foley Square, near the Brooklyn Bridge, by late morning.
Women's March co-leader Tamika Mallory. Kamala Harris of California and Rep. Alexandria Ocasio-Cortez of NY.
But for the third straight year, marchers were flocking to rallies in Washington's Freedom Plaza, New York and elsewhere Saturday.
Loomer, who reportedly met the men at a Home Depot parking lot and persuaded them to join her protest, convinced the men to chant "You're killing us Nancy!" after discovering the congressional leader's door was locked, according to The Daily Beast. "That means we will not let anyone take our rights away - in fact we will expand them".
This year's march has also been roiled by an intense ideological debate.
She said she would "keep opposing Donald Trump and his policies".
"I come every year".
Fewer than 1,200 marched in Chicago, that city's Tribune reported.
As the political movement that grew out of hundreds of loosely affiliated marches in 2017 has grown, divisions have emerged.
Right-wing activist Laura Loomer broke onto the stage during Women's March in NY, accusing the event of anti-Semitism.
We are here to champion ALL women's achievements and advancements.
These marches stem from the ones that started in January 2017 as a display of resistance to Trump's election.
Appearing on the PBS program "Firing Line", hosted by Margaret Hoover, Mallory - who has been dogged by allegations of antisemitism over her strident anti-Israel views and her ties with Nation of Islam leader Louis Farrakhan - declined to affirm that Israeli Jews were native to the land on which they lived.
"The women's march is the real Nazi march", Loomer said.
Ocasio-Cortez told NY marchers that the November election meant "the start of our advocacy". "What we're doing today is we're going to uplift each other and we're going to make sure we stay positive".