You have to join the party at grassroots level from what I understand.

据我的了解，你得由基层组织入党。

《柯林斯英汉双解大词典》

Three families join the party.

三个家庭参加了这个聚会。

youdao

I accepted the box, a gift from Sarah, and asked her to join the party.

我接受了莎拉送的一盒礼物，并请她参加聚会。

youdao

Long-time Pennsylvania Senator Arlen Specter announced he is leaving the Republicans to join the president's Democratic Party.

VOA: special.2009.05.02

Reid told reporters he had been making overtures to Specter to join the Democratic Party for some time, even before the senator from Pennsylvania faced a difficult reelection contest.

VOA: standard.2009.04.28

She inspired me to join the Labour Party and many to join the Conservative Party.

BBC: North East reaction to death of Margaret Thatcher

It therefore announced earlier this summer that a British law firm, Linklaters, would join the party in November.

ECONOMIST: Professional services

More than 7, 000 people have applied to join the party even before its founding congress in Berlin on Sunday, said Petry.

NPR: Anti-Euro Party A Wildcard In German Elections