See the ad network’s documentation for the current object limits, such as the maximum number of campaigns per account, the maximum number of ad groups per campaign, and so on.
Baidu: Each Baidu account can include up to 100 campaigns; 1000 ad groups per campaign; 5000 keywords per ad group; and 50 ads per ad group.
Microsoft Advertising: See "Limits for accounts, campaigns, and ad groups " at https://help.ads.microsoft.com/#apex/ads/en/52001.
Google Ads: See https://support.google.com/google-ads/answer/6372658.
Yahoo Native: See “Object Representation” > “Limits” at https://developer.yahooinc.com/native/guide/objects.html.
Yahoo! Japan Ads: See https://ads-developers.yahoo.co.jp/en/ads-api/developers-guide/value-constraints.html.