$SiteURL = "https://tenant.sharepoint.com/sites/site/siteAA1"

#Add references to SharePoint client assemblies and authenticate to Office 365 site – required for CSOM
Add-Type -Path "C:Program FilesCommon FilesMicrosoft SharedWeb Server Extensions15ISAPIMicrosoft.SharePoint.Client.dll"
Add-Type -Path "C:Program FilesCommon FilesMicrosoft SharedWeb Server Extensions15ISAPIMicrosoft.SharePoint.Client.Runtime.dll"

$User = "admin@tenant.onmicrosoft.com"
$Password = Read-Host -Prompt "Please enter your password" -AsSecureString
$Creds = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($User,$Password)

$Context = New-Object Microsoft.SharePoint.Client.ClientContext($SiteURL)

$Context.Credentials = $Creds

$web = $Context.Web

$Context.Load($web)
$Context.ExecuteQuery()

$web.DeleteObject()
$Context.ExecuteQuery()
Write-Host $web.Title "Site Deleted"

#enter the site collection url
$SiteURL = "https://tenant.sharepoint.com/sites/site/"


#Add references to SharePoint client assemblies and authenticate to Office 365 site – required for CSOM
Add-Type -Path "C:Program FilesCommon FilesMicrosoft SharedWeb Server Extensions15ISAPIMicrosoft.SharePoint.Client.dll"
Add-Type -Path "C:Program FilesCommon FilesMicrosoft SharedWeb Server Extensions15ISAPIMicrosoft.SharePoint.Client.Runtime.dll"

$User = "admin@tenant.onmicrosoft.com"
$Password = Read-Host -Prompt "Please enter your password" -AsSecureString
$Creds = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($User,$Password)

$Context = New-Object Microsoft.SharePoint.Client.ClientContext($SiteURL)
$Context.Credentials = $Creds

#enter server relative path of the subsite in the array
#for first level subsite, it will be "siteaa1" - url would be ""https://tenant.sharepoint.com/sites/site/siteaa1"
#for second level subsite, it will be "subsite/siteaa1" - url would be ""https://tenant.sharepoint.com/sites/site/subsite/siteaa1"

$array = @("siteaaa1", "siteaaa2", "siteaaa3")
for ($i=0; $i -lt $array.length; $i++)
{

    $web = $Context.Site.OpenWeb($array[$i]);

    $Context.Load($web)
    $Context.ExecuteQuery()

    $web.DeleteObject()
    $Context.ExecuteQuery()
    Write-Host $web.Title "Site Deleted"

}